Back in WIn98\Me times we can dublicate network connections and make virual LAN on one PC - without Steam Remote Play Together, without Hamachi and etc. Without second PC.
Probably, this can be done with IPX wrapper bundled with GOG release (or downloaded from ofsite). I dont know how to do it.

www.war2.ru
Ask there. I think it is possible to make a null-bot, but it require some code-working and i dont think someone have enough enthusiasm for that. No good reason. Make bot-allies to skirmish - maybe. but that less possible technically.

Just make map and give opponent (computer) farm without any units, game will finish when u destroy this farm

I swear I recall being able to make opponents that weren't aggressive.

I forgot about it, just set up ai from land_attack to passive