In case it is helpful. I have just got BA to switch my flight so that we are now travelling via Boston.
It does mean an overnight there (rather than our previous overnight at LHR) and retains the 5 nights of hotels so that we should get our double tier points.

They waived any change fees (including for the hotel) although is costing us a pretty penny extra for the hotel in Boston & I am sure we will probably end up spending a bit extra that night too (oops).

Slightly more frustratingly it does mean having to get to Jersey even earlier for our connecting flight.