not if they are similar to existing ones.
for example, I am thinking of one same to yuffie's conformer but that inflict magic damage, rather than physical
To do that you'd have to create a new upper nybble consideration function which is more complicated. The game could use a magical version of those multipliers for overall balance, yes? Without further modification, it'd be forced to use damage formula X1, but that could always be re-handled.
Based on the existing formulae, here's what's possible:
Damage Physical Magical
Standard yes yes
Special yes yes (albeit unused)
Standard w/Multipliers kinda no
Special w/Multipliers no no
The multipliers would only multiply damage done by the special formulae which could make them less predictable. Only multipliers 0, 1, and 2 would have any effect, but then the results like MHP - HP wouldn't be as exact anymore. We could probably do without that whole category.
Standard w/Multipliers defaults to standard formula X1. It can be forcibly changed to use one of the others, but it's still universal to the multipliers category.