Blindness: I have no strong opinion on the matter, but IMHO applying the effect as per spell description (without stacking the penalties) should be the default (again, by the 'description = intent' criterion of the Fixpack).
I'd like to point out this "fix" would cause a sort of "compatibility issue" with
SR, and possibly with any other spell mod (e.g. Spellpack?). Right know I've corrected all the descriptions to match vanilla's opcode (if I'm not wrong this wasn't addressed by Fixpack, was it?), and if the intended behaviour is restored I need to know it (aka
SR needs to take that into account) or the fixed descriptions would suddenly become "unfixed".
I have no particular preference between -10
thac0 and -4
thac0/
AC, but if you ask me this is an unnecessary fix, unlike making multiple blindness opcode not stack, which is indeed a must.
Apply Casting Level Bonus: does the opcode do anything in vanilla? If not, then it's clearly a fix and should be made to work by default, otherwise, it depends on what it did in vanilla and if any mod is willingly using its vanilla effect rather than the IESDP effect.
I'm currently using Taimon's code to make this opcode work. I use it in the upcoming IR V3 for both Potion of Power (to make it grant +2 to caster lvl as per
PnP) and Amulet of Power. Is there any difference bewteen the two fixes? The opcode didn't worked at all in vanilla, thus fixing it by default should be fine as long as it works as inteded.