All good questions, @Old_Scientist.
The only pointer I can help with is the Samsung defrost strategy, as outlined in Samsung R32 ASHPs - when is a defrost not a defrost?
This suggests that OAT is definitely a factor in defrost cycle initiation.
Personally I’d be wary of doing anything that might override defrost initiation - that L2 line (the usual defrost start condition) extends up indefinitely, and you don’t know when the COND_OUT sensor is seeing -6degC or below (unless you have monitoring equipment on it). So fooling the OAT sensor may save you lots of money most of the time, but wreck your HP if you do need a defrost but somehow prevent it happening…