So that answers my next question, I guess, which is Is it normal to repaint armies? Like if I suddenly decided I wanted my models to be Imperial Fists instead of a chapter of my own design.
Entire armies? I suppose you could. But for most people, they'll spend enough time painting one army that painting all over again seems... daunting. I have one friend who has painted his Marines in neutral colors, to allow him to play whichever codex he feels like, without confusing his opponents. "But they looked like Blood Angels!"
Also, tomorrow is your 40k night, right?
Indeed. Open to all, come by and introduce yourself.