I had planned on adding a few glorious looking mods onto a save-game that I favor, but I wanted to make sure that they didn't require you to make a new character first.

List:
Tamriel Rebuilt
Apostates to Oblivion
To Serve Sithis
Antares Tribunal Main Quest
The Underground


Thanks for any input!

Although I have only tried Tamriel Rebuilt out of all of those, all of them should be fine to add to your save game. Just make sure you backup your save game first, in case you don't want the mods anymore.

Antares Tribunal Main Quest sticks out as one that would depend on how far you've done the Tribunal Main Quest. Also, I'd guess the readmes would give you a qualified answer for many of them, if you haven't checked them already.

According to Antares, his mod can be used at any time, even after finishing Tribunal.

Even if you're right in the middle of the original Tribunal main quest?
I'm guessing there would also be a difference between 'can' and 'want to'.

Yeah his is silly, I already did the Tribunal Main Quest and I'm gonna play it off as reality warping in the story, and some Trickster god is behind it.