You could ask the bank but I imagine if it was taken out as a BTL mortgage then unlikely. Does pose an interesting question though and if you were to apply to another bank as a switcher would they know it was originally a btl. Helps that your other property is mortgage free
Actually I'm not all that sure! A lot of PPR's with trackers - people renting them out and bank couldn't force a BTL interest rate so was thinking in reverse. Best idea is to ask your bank and failing that try switching to another bank and see what happens