There is a birthday rule in California for Medicare supplement/medigap enrollees allowing for a special election period. If you find that the premium for your current medigap/Medicare supplement plan is getting too high for you, since medigap policies are defined by Medicare, there may be another carrier whose premium for the same plan you are on is lower. Or you may decide to change to a different medigap/Medicare supplement plan. You are allowed to apply to the new carrier within within the 30 days following your birthday to be effective on the 1st of the following month as a guaranteed issue (no health history underwriting).
Medicare supplements are defined by Medicare and cannot be changed by a carrier. All carriers can offer the same Plan F or Plan N at different premiums, but the plan benefits will not differ.
However, if you decide to “go down the letters of the alphabet” i.e., from a Plan F to a Plan N, you will not be able to go back up the letters of the alphabet to a Plan F without undergoing health history underwriting.