Can you change attack dice rolls?

Can you change attack dice rolls from 1d20 to 1d100 or can you make it so that whenever you get a roll of 1 it should change it to a 2?

This is doable with nwnx, but changing 1d20 do 1d100 will need to be followed with a lot of rebalancing of all the other stats. However, nwnx2 (for 1.69) development is mostly dead, so if you lack the skills to do it yourself, you’ll need to motivate someone, likely from the nwnx:ee group. If anyone wants this for EE, they can just file a request at github.com/nwnxee/unified/issues

The rebalance would probably be too annoying. Can you instead just change the dice roll from 1 to 2 and 20 to 19 if you roll those numbers?

Yes (you could even change the distribution so that different numbers have different probabilities), but the nwnx limitations still exist - it is multiplayer only. In 1.69, there is nwncx, which works in singleplayer (windows only), but very few people are able to write extensions for it as it requires some files that bioware gave to select people under NDA. (and also requires reverse engineering, assembly and c++ knowledge)

I have disassembled other games before to change stuff I didn’t like, but I can’t figure out how to find the particular memory region that handles dice rolls in NWN.

I was scrolling and saw this post—kinda made me think about how much fun it is to mess with dice rolls in games. Switching from a 1d20 to a 1d100 or tweaking rolls, like turning a 1 into a 2, can totally change the vibe of the game. I’ve tried stuff like this before just for fun.
If you wanna test out ideas like that without diving into a full setup, check out flipsimu.com. I’ve used it to roll dice with all kinds of sides and even rig some rolls to see how they’d play out.