I am new to using GoG. How would I go about modding the offline versions of GoG games? Is it even possible? I want to mod Battlefront II and SimCity 4. I have them installed on my offline PC with the Galaxy free installers.

Absolutely possible, and as far as I'm aware there is no difference between "online" and "offline" versions of GOG games. Just find your install folder (that'll be the Games section of the GOG Galaxy install folder) and find the game you want to mod. You can mod it there or copy the installation to somewhere else if you like. Which is to say, the same way you'd mod any game that doesn't have DRM.

Entirely possible.

Unless you mean mods exclusive to say Steam Workshop, in which case shrug.

Starbound, Sim City 3000 and 4, and many more are valid modding targets.

What they ^^ said.

For specific help with those two games, take a peek in the respective subfora here on gOg:

https://www.gog.com/forum/simcity_series#1528624272
https://www.gog.com/forum/star_wars_battlefront_ii#1528201337

Good luck.

it's all possible, I mod unreal tournament, quake arena, stalker, and much more and never had issues with any of them. even with the online installers. so you are A.O.K! enjoy.

And btw if you are into quake 3 arena... I did this little guide.

https://www.gog.com/forum/quake_series/quake_3_arena_hd_resolution_texture_pack_small_fixes_links_inside

Check out Nexus mods to see if they have been modded and follow instructions.

I know,Nexus is the KING site for mods.

Yes, you can mod without problems. One warning though. If you have GOG Galaxy, and the game is present in there, disable auto-updates in it. Otherwise, Galaxy will check the game files and restore them to the original form, i.e. remove any mods. Encountered this problem with Return to Castle Wolfenstein.

Just install the games via the offline installers that you can access by clicking on the game you've bought on your digital shelf that you can access on your account.

You can mod every game on GOG and there are no restrictions. Feel free to mod or hack (same thing, really) any game to your hearts content and right out of the box. Don't ask me what I've did to the GOG version of Gothic 2 :>.

Should you have problems with Battlefront II and especially SimCity 4 since I have some experience with it modding several different versions of the game and know all sorts of problems about it, feel free to hit me up in chat. Nexus is the second choice if the game is famous within the nexus modding community (ie. a game like Skyrim) use MO2 instead first due to its sandbox nature so you don't break games while modding, debugging and testing regardless if you're a user or a modder.

Its way more complex compared to using Vortex but if MO2 supports one of your games absolutely use that client instead. MO2 is primarily used for Bethesda/Bryo/Creation Engine games so if your game doesn't fall into that category use Vortex instead.

Not to "rain on your parade" too much/for bad reasons, but the thread is 2 years old and was bumped by a spammer(OP might not even be still on the forums).

Oh, two months ago I've made the same mistake, had a good laugh though.

It happens :)

Thanks for this 2 years late answer, it is just the information that I need just now, and it was a main issue to consider on purchasing GoG Elder Scrolls saga. Thanks a lot again.

By the way, I have Morrowind available thru the Bethesda launcher, and I wonder if it can be modded. Is that possible? Thx