I want to change the default in game messages and I believe they're located in the qwprogs.dat file. What program do I need to edit it?

Anyone :rolleyes:

It depends on the mod. You will need the sourcecode for QuakeWorld's qc (QuakeC) or the one for KTX or for KTPro or whatever you want to play. The compilation process is different I think. For plain QW fteqcc should do. Dunno about those hip and modern .qvm files.