Primaries are tough since you can only choose the candidate in your party to run in the general, but writing in or temporarily switching parties and voting Democrat are your best options. Registering 3rd party isn’t a good idea because unless they’re competitive in your area you’ll only get a provisional ballot (basically a participation questionnaire, you don’t even vote for a candidate). However, if you write-in a third party, make sure you get a lot of support behind them