If you are just editing for you own use there is no reason not to edit the source files. Much easier than making a mod. As long as you have a backup of the original file so you can 'restore to default' at any time.
You can overwrite almost any game attribute from within a custom map
without editing a source file. The changes will only apply while the map is running. Not so easy on orig RAS maps. Can be done, but very complicated. To be brief, you would need a line of code within the map you are running to execute some code within your mod. This means adding code to all maps you want the mod code to run in thus editing source files. Even if you put in fail safes clauses to catch exceptions it's still a clunky method. i did this once with an 'All Combos' mods and I think I replaced BladeInit.py with a modded version so as to execute the code without having to do all the maps. You have to be careful though and make it so the code won't cause exceptions.
There is a very good reason why mods should alter source files as a very last resort. While it is true that the BODLoader will restore replaced files in the Uninstall routine, the danger comes when you use this on more than one mod at a time. So you install one mods which overwrites say, Reference.py. Fine. But then you install another that does the same. The second mod will store a backup of not the orig file but the version that the first mod installed. Can of worms.
e.g. Someone installs my All Combos mod. All will work well until you install another mod that also replaces BladeInit.py. Nothing bad will happen except the All Combos mod will be disabled. Uninstall/Install All Combos will bring it back, but will disable the new mod. You can't use them both at the same time in other words.
See what I mean about complicated?
But as I say, edit away if it's just for your own devices.