Mark Hansen wrote:

Or, are you supposed to maintain your transponder code until changed
by ATC or you cancel IFR - even if radar service is terminated?

Well in the ADIZ you darn well better keep squawking that discrete
code to the ground even if you cancel IFR (ATC will usually warn
you about this...violations are a pain in the butt for them too).

It's pretty standard everywhere else. I've never been told to
squawk VFR while IFR even without radar service.