simple enough question.
i was reading through burning bright and the main chaircter seams to have the ability to make new spell effects up on the fly. though this dose seem to be rather taxeing on him.
is there any rule canon for this trice? or is it just a fiction fluff trick, as i am pretty sure it is.

Having not read "Burning Bright," I'm going to answer this in two parts.

There is no canon rule which I'm familiar with for making new spell effects on the fly. The process is explained is fairly good detail about exactly how long it takes a mage or shaman to learn a new spell and the necessary work for creating an effect which does not exist.

That said, some GMs, myself included, will allow for cinematic changes. You cast fireball, but this time you want the fire to glow green...sure, the mechanics of damage etc stay the same but I need you to give up a couple of successes from your Sorcery test to make the modification.

Edit: This is available in SR4 as well as an optional rule...with mention of more optional rules to be added in future releases.

Kenson's a big fan of magic. In a lot of ways, (rather unfortunately if you ask me) he's become the "Magic Guy" of their creative team -- both in terms of the novels he writes, and the sourcebooks themselves. Talon slinging around mojo left and right and making it up as he goes is probably something Kenson wanted to put into the rules, that calmer heads didn't let happen.

There's a set of rules on his webpages for all sorts of magic-related stuff (I'm not sure of the address, and quite frankly don't quite care enough to Google it myself, but a quick search should find it for you), and maybe this "casting on the fly" stuff is in there somewhere.

The trouble with making up spells on the fly in Shadowrun is that you have to pay for them with Karma.
That being said, you could have him.
Make a spell design roll to figure out the appropriate formula as a Complex action. The number of successes would determine the maximum force of the spell.
Cast the spell as normal but use force as drain instead of F/2, or make it automatically physical drain. You could also say that it is a Metamagic Feat and the force of the spell can not be higher than his initiation grade.
Still there might some difficulties in allowing the character acess to unlimited spells.

Could you specify "spell effects," or quote one of the relevant passages?

lets see. shape wood, ram,touch >lock, agoney, and spirit bolt.
spell effects he did on the fly.

Burning Bright is my favorate Shadowrun Novel, but one thing about hte novels i general is, you are never told what spells the characters know, they just sling them around. Maybe they are taught to manipulate magic in a certain way, then later learn to futher modify this method to futher their goals. Who knows but the Authors
As for Agony, I think that was an empty threat (if you were thining of the moment were he threatens the Flesh form) Teller admits to Seeks-the-Moon he doesnt know any spells like the one he described to the flesh form. His Ram/Wrech vs Locks could be just that, though I think it was described as a Power Bolt in the book. Shape Wood could be from his time in the FBI for all we know.
From Bug City pp 146 - "He knows a smattering of combat spells, but is focused primarily in the areas of investigation and detection."

thing is that how a specific spell appears when cast is never set in the text of the diffrent effect.

one mages unlocking spell may well look like some other ones power bolt, while a diffrent take may well just be a clap and the lock pops open. i would guess it depends as much on the mage and his mood then the spell itself. maybe the signature of the mage plays a part to?

allso, this is from a novel, we all know that when writing novels, the last thing they worry about is for the text to follow the rules to the letter...

What are the rules for attacks on the fly for deckers? <gifted all my books away recently>

rating equal to dice allocated from hacking pool (max equal to programming skill).

damage level based on a computer skill test vs host security rating, one level pr success (1-L,2-M,3-S,4-D)...

seems straight forward enough

There is a lot of room in the magic system for exactly this type of spellcasting. It would be pretty karma intensive to get any good at it, but I could see it as knowing certain elemental effects of each spell.

Fire, Ice, Sand, Air, Earth, Flesh, etc... That's just for the effect, almost like an elemental mastery.

The second set of NECESSARY skills would be the five spell casting types.

Combat, Health, Detection, Manipulation, (what's the fifth one?).

From there I could see it possible to make spells up on the fly. Isn't this like the magic spheres from some other fantasy novel or something?

Unfortunately, you'd have to house rule the fiznuck out of it to use it. There's no rules (as far as SR3) to make stuff up on the go.

Basically, it's to maintain game balance. If everyone was mages running around, throwing each and every spell out of the Grimoire at their convenience, why would anyone play anything else? The Street Sams are stuck with the cyberwear in their body, they can't make cyberwear up on the fly.

CONSIDER THIS:

Spells are thoroughly researched before execution, because they actually bend mana to your will. Without proper research, there isn't the fine control over mana. There's a good change your hellblast would backfire, your heal spell would kill someone and your physical barrier would lop your own legs off.

If I were GMing, I might allow off-the-cuff spellcasting. However, they'd only try it once of twice before they found out it was more trouble than it was worth.