significant : modify all parameters (guideline, penetration, range, duration, target) of a formulaic as soon as the sum of modification is in -1/+1 magnitude changes :
example : changing an InVi 5 effect1 to an InVi10 effect2 with new guideline and RDT fitting in the level 10 budget
total : similar behavior with additionnal parameters (technique, form) in the +2 magnitude range :
example : changing an InVi 5 effect1 to an MuTe15 effect3 with new guideline and RDT fitting in the level 15 budget
Solution 2
significant : modify one parameter only or boost the power (but what about guideline?)
total :modify all parameters or boost the power (but what about guideline?)
I have an specific example in mind:
Can I change "Sense the nature of the vis" InVi5 Base:4 R:Touch 1, D:Mom, T: Ind to a "Detect vis" InVi5 Base: 1; R: Smell 2, D:Sun 2 ?
With total change guideline, I would say yes. With significant change, I'm confused : not changing Te/Fo, not power boost, but guideline and parameter change.
One thing to keep in mind is that a MuVi effect is designed to change every spell (or at least a large class of spells) in one specific way. For example, it might make every spell last longer, or have an opposite effect.
So one should probably phrase the question as: Is there a specific change, that can be applied to all spells or to a large class of spells, and if applied to Sense the Nature of Vis changes it to Detect Vis? And if so, is it a significant or total change?
The problem I see with changing a spell that uses one InVi guideline, at R:Touch, D:Smell, into another using an unrelated InVi guideline, at R:Smell, D:Sun is that it's really hard to frame it as one specific change that can apply to a large class of spells.
It changes the Range, and the Duration, and the guideline.
I would certainly allow a "significant" MuVi spell to change R:Touch to R:Smell.
I would certainly allow a "total" MuVi spell to change D:Mom to D:Sun.
I would probably allow a "total" MuVi spell, with an extra magnitude for the extra effect, to change a R:Touch, D:Mom spell to R:Smell, D:Sun (note this combines two different changes, one total and one significant, so it's "priced" as the first plus a magnitude of the second): let's call it Archmagus' Multifold Extension of Vim: extends the Range of any Vim spell by two magnitudes, and the Duration by one.
I am hard-pressed to find a specific change that can apply to a large class of spells, and that in this specific case case changes the Detect the presence of Vis guideline into Discern the Art of Vis. Maybe Wizard's Prerequiisite Learning? Changing any Intellego spell that detects a specific quality in an object, to an Intellego spell that detects the presence of that specific type of object? Mmm. Sounds very iffy to me, and in any case this is a 3-magnitude change, requiring a Perdo requisite to shunt out the extra magical energy.
I would be very, very unlikely to allow a single spell that combines Archmagus Multifold Extension of Vim with Wizard's Prerequisite Learning, even by paying an extra magnitude on top of the higher of the two spells.
However... why not simply cast the InVi Base 1 effect at R:Touch, D:Conc (so total InVi level 3), extend its range by one magnitude with a level 4 Wizard's Reach (MuVi level 4) and Maintain the not-so-Demanding Spell for D:Sun (ReVi level 5, works on any level 4 D:Conc spell)? It's probably cheaper, and doable spontaneously without fatigue even by a (sufficiently specialized) starting magus without any particular Virtues, at least outside hostile Auras.
Thanks for you help, my comprehension problem seems to be:
with a total change, if I change technique and form, this means, I change the guideline.
does the mutated spell have to stay on the same RDT and stay at the same level ?