To break and pay the rate diff loss to the bank plus FEES. or switch the loan to a variable which incur's a switching FEE only, giving a cheaper option. the terminoligy is the clue here and worth investigating I did this with one of the big four 13 years ago but expect there have been policy changes since.
security substitution sounds good tho.
Good luck and if you push hard enough you should get a fair outcome.
