EGM has shown it's possible to add existing temporary/conditional squad mates as full time members, and I'm wondering if anyone knows of any resources available to show how to do the same for Anderson. He has his own full skill tree and all of his files are in the vanilla game PCC and AFCs vs the Armax Arena squad mates that are only available via the Citadel DLC, which should make things easier. If anyone could point me in the right direction that'd be much appreciated.
He's on Earth and unavailable for the entire game after the prologue. After that, you see him in London for a bit, but then not again until he dies. There's really no time there, and inserting a squadmate is a ridiculous amount of highly-advanced modding. It's not something you should even consider attempting until you have a good amount of experience under your belt.
No doubt it wouldn't be lore friendly to add him as a squad mate (except maybe Priority: Earth). It would just be something like in EGM where you can choose to have Wrex, Zaeed, Miranda, etc. on missions when it doesn't make sense story-wise for the fun of it. I'm also just a fan of Anderson as a character and imo he was way underutilized throughout the trilogy, this would be a cool way to fix that.