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So, the point here is, what effect does adding a theme/tag to a system actually have (and could you please give me some details on what each tag means/does?), and is there a way for me to have this sort of organic salvage/exploration generation I'm looking for in my system without me having to specify all the details? If not, is this something you could implement in the future?
Anyways, thanks for your time and all your effort on this awesome mod!
The "systemTags" option just simply applies whatever tags you specify to the star system - and nothing more. What each tag represents
completely depends on how the game treats a star system with a specific tag. The most frequent way they get used is for preventing missions from spawning on said star system (e.g. "theme_hidden", "theme_unsafe", etc.), for allowing other missions to spawn within them (e.g. "theme_interesting" or "has_coronal_tap" for certain contract bounties), and for setting star systems as Core World systems (the "isCoreWorldSystem" option already does this by applying the "theme_core" tag and either "theme_core_unpopulated" or "theme_core_populated" depending on faction existence). Other than those things, I don't know all the exact details about each and every tag, but it is safe to assume that system objects do not spawn due to any specific system tag.
As for adding randomly-generated salvage within custom star systems, that is something that I can look into for a future update, if it's feasible to implement cleanly. However, I'm currently just waiting for the next Starsector update before I'll consider adding any more features to this mod, so I wouldn't expect random salvage to become a thing for a while, if at all.