Looking for Tutorial on how to Properly export textures and replace Melee in L4D2

Hello, well i modeled a Scythe which i want to use in Left 4 Dead 2. Then i textured in Substance Painter, note that i have four Texturesets so i can better apply my materials. Now im stuck at the point where i dont know if i need to merge all four texturesets to one big, if i want to use it in the source engine, or if i can just render each texture and assign them later on.

The next problem is, i dont know how to replace Melee weapon models. I saw some guides but most of them are outdated and the SMD Import/Export (including cannonfodder) does not work in 3DSMax 2019. Well shit, help is appreciated. Im looking for tutorials in first place.