IMO the reason behind mods disabling achievements is to preserve the "value" of achievements. The idea is that, the developers come up with the achievements based on the game that they make, so to achieve them you have to play by the developers' rules, using what they give you.
Right, my point exactly.
In this case, this dice rolling thing is for GM mode, right?
I think he was asking for it to be an option for regular play. "can [I] bypass the built in dice roller and use real life dice and just put in the number manually.
If not, can this be done in the gm mode"
In other words he asked "if you can not (do it in the normal campaign), can this be done in the GM mode".