I'd like to modify the spell fumbles rules, but in a balanced way, and the 'swashbuckling' skill is a good reference.
When you do a weapon fumble, you can make a 'swashbuckling' roll to evade it, then I am thinking of use a SCSM roll with a modifier for the same. I think the modifier could be -50, and then allow to player decide if he wants a SCSM roll to evade it, because as with any skill roll, you can get worse the situation (as a 'total failure' with swashbuckling, 'stun removal', etc.), remember that you can roll the spell fumble with the double or triple of your SCSM modifiers, BUT then, and this is important, I'd not include the -50 to modifier, only the usual modifiers (as PP used).
As note we don't use the 'PP used' as SCSM trigger, but if you need to roll a SCSM for any other reason (armor, not voice, etc.) the we add that modifier. Too we don't require a SCSM if your SCSM armor penalty is +0 (trascend armor), because is tedious (the 'PP used' trigger is tedious too) and we see it not appropriate (Paladins rolling for every spell they cast?).
But, how about the 'spell fumble evading' rule, what mod. you would use?.