It's definitely possible, and the quicker you talk to them, the more likely they'll be willing to do it.

However, one time a concierge accidentally cancelled a Y FP booking I wanted (this was via email, so it was DEFINITELY their fault, as I was using email to ensure everything was clear), and they rebooked me right into full J, as the flight was now Y0. They justified it as "well we gave you your comp-up early", which was fine for me, but clearly there were limits with what they could do on a technical level, even when it's their fault.