TRS4 form affecting mortgage rate?

If you submit a TRS4 to revenue stating that an existing mortgage you have no longer qualifies for TRS, how likely is it that the lender will knock you off your current interest rate and attempt to place you on a new one?

There is no link between TRS and your interest rate.

The ability to knock you off your current interest rate will be determined by the Terms and Conditions of your mortgage.

Will do....that's going to take a while.

I understand that TRS is a Revenue issue and your agreement with your lender is another but surely both tie together when Revenue instructs the lender not to offer TRS on the basis that its not the owners principal residence any more?
Maybe....maybe not...

I think if it is part of the T&Cs that the mortgage is for a PPR only, and doesn't apply to an investment property, then it wouldn't be just a simple rate change. You would have to switch to a Buy-To-Let Mortgage.

I'm not sure the bank would care particularly, but you might consider if it is the best option for you to remortgage.