Mortals and Magic Option

This option assumes that the only way mortals can use magic is by channeling the energy through their own body, which subjects them to a spell tax. Sorcerous skills can be used without channeling magic, as normal (not open ended) skills like alchemy, aura reading, circination, even sorcery for the purpose of studying (not casting) spells.
This option also assumes that all gifted mortals have the ability to learn any type of magic. The gifted are simply channelers, it is the skills they learn that determine how their magic is put to use. Any failed attempt at channeling is subjected to spell failure, any use of magic is subject to a may not.

(Altered from Magic Burner pgs 48-54)
Instead of Sorcery, this system allows the gifted one to infuse their normal skills with magic (making it open ended at the cost of a spell tax), as long as the skill is in one of the practical magic schools he knows (either the first listed skill in each of his lifepaths, one that he has purchased in burning, or one he has adopted in game) Note that the Sorcerous school is no longer required to perform Practical Magic and therefore, no longer free to learn. It is priced the same as the Academic school (16 rps), and is just as difficult to learn in game ( adoption obstacle of 8 ).
As an example: Garek Hall is a noble sorcerer (Born Noble, Noble Page, Arcane Devotee, > City Sorcerer) His first listed skills (and type) are: Riding (Physical) from Noble Page, Calligraphy (Academic) from Arcane Devotee, and Sorcery (Sorcerous) from City Sorcerer.
This grants him practical magic in The schools/realms of Physical, Academic, and Sorcerous skills allowing him to channel magic into any of those types of skills he knows (no channeling with beginners luck).
If Garek is facing an Ob 3 riding test (moderate journey, roads, fast as possible) he could channel magic into his normal riding skill of B3 (making it open ended), it would require an Ob 3 spell tax to do so. Garek gets to roll three open ended dice (plus one normal die for using a riding horse) against his Ob 3 riding test.
Once channeling has started, it must be continued throughout the series of tests unless the gifted one chooses to stop, surrender, fails a steel test, or takes damage (suffers a may not). Note that any of these actions runs the risks of spell failure.

I like it. It’s a relatively simple adjustment, and keeps things cool for mages.

You might consider dropping the RP prices by about 25-50% to reflect the weaker effects, and dropping the adoption Obs by 1-3 for the same reason, but even without those tweaks it sounds fun and looks like it will add game.

Is “Practical Magic” a training skill, or an automatic consequence of being Gifted?

It’s an automatic response to being Gifted which is why it taps into the first skill type of each lifepath, they are the ones that are stressed as being important to it. And just like in the book, only the first listed skill matters.
(If Garek had taken Noble Student instead of Noble Page he would only have Academic and Sorcerous schools as his free practical schools since Writing (Academic) is the first listed skill in that lifepath.

It is also the assumption that all forms of magic available in the MaBu be available, but controlled by their own individual skills.

Sorcery is used to study, abstract, distill and channel magic formulas into standard sorcery spells.

Spell Weaving is used to channel magic into the users Art Magic, allowing the gifted one to weave a little magic into their very being while creating spells that are uniquely their own.

Alchemy is used, not only to collect and distill ingredients for potions, but when channelled, it is used to create and empower magic potions as well (normal alchemy could be used to create a lubricant to reduce the draw time for your sword, magical alchemy could be used to make an oil that lets your sword affect spirits).

Enchanting can be used to prepare items for enchanting (purifying the vessel about to be named) as well as magically charging (or recharging) those enchanted items.

Spirit Binding is used to command spirits

Summoning is used to summon and make pacts with demons.

Circination is used to draw specific circles, gates, and traps, for use with and against spirits, demons, and other supernatural entities.

Necromancy is the skill used by Death Artists to reanimated and control their dead minions.

(Getting Around Being Gifted)
There are ways that a talented normal with sorcerous skills could get around the need of being Gifted to channel magic. Through careful use of the normal use of Circination, Spirit Binding, and Enchanting it would be possible to inscribe a spirit trap upon the hilt of a superior quality sword, binding the spirit within while enchanting the sword by drawing upon the essence of the spirit within instead of the enchanted channeling his own.

Antecedents with magical properties harvested from immortal beings, (or the souls of mortal ones) could be used in place of a gifted channeler.
Some, like the Ebony Shunt (made from the tounge of a Black Troll) are used to aid and protect the gifted ones (in the case of the Ebon Shunt, from spell tax).

Many a mortal have sought out ways to gain or even increase their own power at the expense of others through such means as sacrifice, torture, and unholy alliance or pacts with demons or even the elder gods, just waiting for another foolish mortal to corrupt.
Magic always carries a mortal price, some pay it slowly over time, eventually subcomming to the sickness. Other pay with the blood of innocents, while some pay with their very soul.
But sooner or later, everyone pays!

I don’t own the magic burner, but the above is rather video-gamish and a-historical use of the terms. -mancy is derived from greek which translates as divination. Necromancy was divination by means of dead spirits or in the entrails of animal (and sometimes human!) victims. So in a way a type of spirit binding and summoning. Another historical example would be geomancy which would have been divination by means of rocks (or even rock spirits). All of the primitive and sometimes downright disgusting forms of divination all gave way to the mathematical and loftier means of divination, astrology. If only because this new -mancy required learning and skill and could not just be done by some old crone pulling the innards out of a bird and reading the pattern and splatter on the concrete.

In a fighting style video game like Diablo or D&D, I suppose geomancy is raising rock monsters and necromancy is the raising of dead monsters, but given the beautiful tolkienian elements of BW, I personally, would rather not see the skills described as such. Obviously, there is some heavy overlap of Tolkien with L.Guin and ‘gifted’ type magic in the BW ruleset via EarthSea. And her use of necromancy blurs the line a bit, but even Ged’s disastrous use of necromancy, with his unplanned releasing of the shadow, was an attempt to summon a spirit to converse with, not raise an army of skeletons.

Necromancy works well enough for my purposes (having seperate skills for each type of magic instead of Sorcery being the single skill for all magic) but if you have an alternative suggestion, I would certainly consider it.

“Death Art”

Both are good points, Death Art as the Skill, and allow Necromancy as a form of divination similar to Astrology for linked tests and FoRKs and Rune Casting for revealing another’s fate.
(The linked test wouldn’t require channelling, FoRKing and Pronouning Fate would)