My primary home is paid off and I'd like to port my loan from my second home to my primary so I can write off the interest. My primary home is worth a lot more than the loan. I have a great rate and don't want to lose it and would like more tax write offs.
Assuming this is a US question - The recent change in tax code took away deductibility for HELOCs under certain conditions, and lowered the total loan balance on homes that can be deducted. For loans originated after 12/16/17, it's $750K, before that, $1.1M.
You had, and still have, the ability to take a deduction for your second home.
(If the facts change due to an edit, my answer will need an edit as well)