A few warez releasing groups did this, it was uncommon on PS1 in my experience because it didn't take long for anyone with a PC and a CD burner to figure out how to do it for themselves (you could still rent video games in those days). Quite a lot of the Dreamcast repacks have modified loader screens, and I saw it quite a lot on PS1 to PSP conversions before I learned how to do that myself.
Unico PLAY are no doubt long gone, this is a 20 year old scene were talking about, and many people didn't get Internet until late 1990s/early 2000s, so there's probably not much information about them in the public domain.
There's a couple of sites where you might find out more, but GBATemp rules prohibit naming them.