so I need the patch01.gs1 file in the same folder as all.gsc and not replacing it.
What are the corresponding .MD files for the howitzer, mortar and multibarrelled cannon called?
PSM.MD Multi barrel
If you are unsure about the confusing MD names, look up which is which is in ALL.GSC/TEXT/MDLIST.txt
Also, if I tire of this modification and want to revert back to normal, can I do that just by obliterating the patch01 file?
Never change ALL.GSC, there is no need to do so, since the patch01.gs1 and or mods01.gs1,... will overwrite whatever is defined in ALL.GSC