The
old trainride intro from very early in development already mentions Dr Breen by name.
These vignettes were made to establish the backstory and sense of locations, and that's done before building them, thus the vignettes are very old. One is dated 2000, they are likely from the same time period. So, we're talking very early production (or pre-production even).
It's pointless to ask "when Consul evolved into Breen". Consul didn't "become" Breen. He was already named Breen during early production. The vestigal "Consul" - which is a
title - was kept until it was phased out in favour of "Administrator". There will never, ever be a direct answer saying that "on this date or that, we officially christened him as Administrator and stopped calling him Consul".
Because that's not how things worked.