The Catch.
Leaving the controls - "Locking" of the controls - it needs to specifically refer to "locks" which does NOT include friction systems.
Hot refuelling - refers to "operator" which infers commercial operator. PVT ops do not have operations manuals and/or operators so not applicable or allowed.
Unless your POH allows it then no pilot at the controls would require an STC.
The regs cannot "override" the POH on their own.