Let's say a player adds flavor to a fire spell effect description. For example, instead of the standard gout or ball of fire flying at its target, the player wants to describe it as miniature imp-shaped flames flying from his hands. Without any prerequisite action like a Summoning spell, would a GM have to disallow this, although the player doesn’t intend to have the fire do anything different than normal fire, just look different?
The important part is, that magic comes from what the character believes. Mechanically, there is no difference between fireballs and impballs, and it is a fun variation. I can practically hear the impatient voice of a master wizard telling his (not so talented at fire magic) apprentice "Ok, one more time. Imagine the imps I showed you, they are creatures of fire. Now remember what they looked like, what they felt like. Capture their essence and shape it. Yes! Yes, you did it! You finally conjured a gout of flame. Seems like our trip to the planes of fire really had an imp-act."
I apologise for the pun. Still, things happen a certain way, because your character thinks it is the way they are supposed to happen. If he connects conjuring up fire with the image of an imp, go for it. As a GM, I might even one day go so far as to have you accidentally summon a real imp. Maybe as a harmless pet, a Bob-like companion or a minor villain or all of the above would probably depend on my mood
In a similar vein, a Forzare-type Spirit spell could just pile driver a target with invisible force, but could the same effect (But visible) be done by a Nichtomancer (Shadow-based Focused Practitioner) making a column of solid shadow to smash someone? Or would solid shadow be disallowed?
Why should it be disallowed? You are doing a standard magic action, namely an attack. How you describe it is up to you. Maybe the shadow is only a side effect from the spells energy bending light away, Einstein and all. Maybe the wizard is just conjuring stuff from the nevernever, that looks like shadows, but is actually really solid. Or you are sort of reverse-lasering, instead of focussing a beam of light you are removing everything, creating sort of a light-vacuum effect that results in a force against anything it touches.
Or you simply say "it's magical solid shadow" and roll with it.
Final example: Since Earth magic is linked to Electromagnetism, can an Earth based Block against leaving a zone be created by magneto-gravitically manipulating a flock of pigeons (who navigate via an ability to sense magnetic North) into kamikaze divebombing the zone borders (Lots of dead pigeons, ew)?
I would allow it, I think. In fact, you would probably even be able to do a quick declaration of a "Flock of Pigeons" and tag it on your spell for more oomph.
Yeah, I'm an odd sort of guy. You're just lucky I erased the post attempt involving spells from a Copromancer...
You're in good company. But what on gods earth is Copromancy?