Well,
http://www.pocketplane.net/mambo/ind...d=92&Itemid=77
There's a mod where one part changes the wizard slayer to 8% start MR, +4% MR with level. WeiDU mods are generally split for each add-on, so you can add just that part. I don't know of any other WS enhancement mods, nor do I know how to change it to 3% per level. I would assume that the editor for classes would be NearInfinity or something like that, but don't know how to use it. This would not require a restart, I think. If it did, you could probably just use Shadowkeeper to change your WS's MR% to whatever would normally be calculated for that level.
BTW, there are ways to make wizard slayers own against mages [img]smile.gif[/img] You'd need to pick up a druid for the heavy stuff, though.
I don't think its possible to make non-humans dual class. Maybe you could pull it off with Shadowkeeper. There is no particular logical rationale why non-humans can't dual class, or why humans can't multi, but 2e D&D is full of that kind of stuff and what's even more annoying is when people try to defend it.