After hours of messing with my 15 year old game. . .

I am playing Arcanum Multiverse Edition and extracted gamelevel.mes from the arcanum4.dat file into \data\rules, where any changes should override the DAT archive. No such luck. Any place I can go with this?

I tried deleting and importing the file using datbuilder, but that was a bust. Is there a tutorial for overwriting a file inside a DAT file? Is there a command that says "override from data files outside the DAT file?"

arcanum4.dat belongs in the \Arcanum\ folder. Try a new dat rebuilt from dat builder and replace the one in there.

Backup the old one for posterity, of course.

I've not noticed such major issues with editing gamelevel.mes and saving the edited file in the /data/rules folder.

The only issue I've noticed is on companions who'll not start with edited skills.
Example : I edited Jayna scheme with bow 1 but she'll still start with melee 1, then she'll level her bow skill as edited.