The way spell resist works now is it reduces the severity or duration of non-damaging offensive spells, like curse, weaken, poison, etc. It also gives you a minimum elemental resistance that doesn't stack with anything. GM resistance = 40 elemental resistance in everything.
http://uo.stratics.com/content/skills/resisting.shtml
Maybe if I add Resistable 0|1 to spells.cfg so that spellStarter will know which ones to check resistance on. Still not sure what I would use as the difficulty for the skill check since I don't know how it works on OSI. Apparently resist skill under 40 is difficult to resist GM mages, so caster Magery must factor into the skill check for resist.
If you want to spell resist to work the old way, you could change all damage types to forced and set Resistable to 1 for every spell.
These ideas are off the top of my head...