Once you delve into it, magic in Shadowrun has a lot of nuances and options to it. Aside from the two big areas of sorcery and conjuring, there are a ton of ways to customize your mage. There are traditions, gaes, and fetishes, each of which have a number of options within them. There's a good reason why every edition of Shadowrun has had to publish a separate book on magic, and it's not because they had a ton of spells they couldn't cram into the main book.
Rather than try to reproduce all of that material in Shadowitz, however, I'm attempting to recreate a lot of the feel these rules and options provide using existing rules, specifically the aspect rules. Since each of these tweaks, in broad terms, gives a bonus with an attached cost or limitation, with a little creativity we should be able to represent nearly all of this material using aspects.
Let's start with the biggie: magical traditions. In the beginning, there were two: hermetic magic and shamanism. Though the game has subsequently expanded this to many other areas, most players who have come up through the SR editions seem most comfortable sticking with these original two. In 15 years of playing this game, I think I played with one voodoo priest once. Every other time the party only had hermetics or shamans.
Hermetics don't need any aspects applied to them in terms of basic tradition. They are the well rounded mages who suffer no penalties and receive no bonuses. Their sorcery has always been a straight roll of the dice, no extra considerations needed.
Shamans, on the other hand, traditionally get a bonus to one kind of spell, a penalty to another kind of spell, and some other behavioral quirk. Wolves might frenzy, dogs can't change their actions once a plan is set, lions need to buy the finest goods, eagles suffer twice the essence loss from cyberware implants, etc. The drawbacks are many and varied, so you need to stay flexible in your mechanical implementation, but it can be done.
The most obvious way to apply the aspect is to make the invoke portion grant a bonus to one spell category and the compel to another, thus giving bonuses and penalties to certain kinds of magic. However, this turns the penalty into something that's optional, and the bonus and penalty granted by a totem can be kept as is (1-3 die bonus or penalty) and active all the time.
The behavioral penalty, however, is fertile ground indeed. Here's where you find material that guides a character's actions, and by extension his identity. A wolf shaman's tendency to frenzy when a member of his pack is hurt tells a lot more about who he is than the fact that he gets +2 dice on combat spells. Here, I think, is where you'll find the best stuff for making tradition-based aspects.
Let's take that wolf drawback: you must pass a willpower check or go into a frenzy when one of your friends is taken out. Reading the entire wolf entry, you find this is because wolf is a pack hunter who shows great loyalty to those he runs with. That attitude is is the thing from which we'll build the totem aspect:
You have been touched by Wolf. It is through him that you learned to talk to the spirits and work magic, and it is his eyes through which you peer when you look into the astral plane. Contact with such a powerful, primal force has left an impression on your own mind, making you aggressive, yet team oriented. Most times you can control the feral urges you carry, and can channel it especially well when working with others you are close with. But when one of your own is hurt the rage boils hot and you sometimes see red and lose control.
Invoke - Gain +2 dice whenever casting a spell that is specifically used in conjunction with a teammate's attack. A fireball might flush opposition out into a kill zone, a manabolt can fell a gunner who has a comrade pinned down, etc. Note that this must directly aid another member of your team; you cannot apply this bonus to every attack against an enemy and claim downed enemies help your side.
Compel - Wolves are pack hunters, but they are also savage in combat. You can remain cool under fire when taking the lead yourself, but when you see one of your own hurt (injured or taken out), you sometimes lose control. When this aspect is compelled you abandon all tactics and become mindlessly aggressive toward the force that felled your friend. You must use the most powerful spells you can cast at full force rating, your most powerful weapon, etc., and attack relentlessly (no hiding behind cover or being cagey) until either you defeat the opponent or spend edge to recover.
Geas are restrictions that mages take in order to preserve or gain magical power. When faced with magic loss, a mage can opt to take a geas instead, and mages seeking to initiate can take one as an ordeal to reduce the cost. I haven't dealt with ordeals in Shadowitz yet because our mage doesn't look like he'll be initiating anytime soon, and I didn't include rules for magic loss because in general I've felt mages have gotten the shaft mechanically speaking (especially because no sam ever had to track ammo in the games I played, but I took drain for every attack I made).
However, even though there's not been a lot of call for these in my games, turning them into aspects doesn't seem like something that would be too difficult. Like traditions above, not every geas need be turned into an aspect. Some, like not being able to cast spells when wearing green, don't need any further mechanics. Is your character in a green jumper? He can't cast spells. Done. No more is needed.
But how about those that involve things that are a little harder to adjudicate. I remember seeing an example once of a geas that restricted access to magic after the mage ate meat. On the surface that's simple. Don't eat meat. Let me ask you though, how many games have you played where the dietary composition of the team ever came up? Do your characters ever eat in game? Sure, the lifestyle guides give you an idea of what their daily fare looks like, but is it ever present? Outside of an ongoing joke that "purple is a terrible flavor" in one of my games where everyone was poor and had to buy flavoring in concentrate and apply it with an eye dropper, people tended to focus on running the shadows. You know, the namesake of the game.
The reason I bring this up is that if eating's not a part of the game, then the mage gets the geas for free. He gets a benefit without any consequence. And while you can put him in a position where he might struggle with it now and again, such as meeting a Johnson who takes offense if you don't eat the steak he bought you, you can only emply that method so many times before it gets ridiculous.
What to do? Make it an aspect. You compel it at some random point in the game after there's been enough down time to assume the mage ate something and when he next summons his magical power you toss the edge chip his way and say it's not working.
Wait, what? No, says the mage. I don't ever eat meat. Well, yes, that's what you think. But if you ask most people today, they'll swear they don't eat rat, but if they've ever eaten a hot dog or a Butterfinger, odds are they had a few rat parts in their past. In the days of processed food and lax production oversight (which is Shadowrun through and through) you can't really say with certainty what's in anything you're eating. Bummer. You ate something with enough animal byproducts that it messed up your mojo for a little bit.
Now stripping a mage of his magic is pretty severe, so giving the player an edge point and then relegating him to a crappy gun skill with a light pistol for the next 24 hours of game time isn't a good trade off. If you're going that route, I suggest making the compel worth more points, maybe even upwards of 4 or more.
Another way of doing it is reducing the penalty for violation. Instead of barring the mage from all sorcery and conjuring tasks for the duration, you could instead inflict an ongoing die penalty. In this case, you should still give a couple extra edge points for invoking the geas, but not as much as if you strip the mage of magic entirely. In this case he's hurt, but he's still functional.
Fetishes are objects that a mage uses to boost his spells. They're similar to foci, except that they're not overtly magical. Instead of tapping into the extra mana that foci bring to a magical process, mages instead learn to use the mundane fetishes to increase their own power. They are parts of the magical process, but are themselves not batteries of mana.
As aspects, fetishes are the opposite of geas. Where geas only have a compel portion, fetishes only have an invoke aspect. There's no downside to using fetishes outside of the fact that you can run out. (Yes, I know some editions have included non-expendable fetishes, but those always seems like cheap foci to me, so I kept fetishes to the expendable variety in my games).
Since fetishes get used up in the casting process, you need some kind of ammo counter. Or, really, you don't. After all, if a fetish aspect gets you a bonus when casting a particular spell, let's just say your edge pool represents your fetish supply. Spend the edge, get the bonus. When you run out of edge, you run out of your fetishes too. If you later get more edge, you've managed to find some more fetish material as well.