This is a common scenario where we 'drop a category'
You fly Day VFR charter in a SE plane to a destination, drop off the pax and come back at night. The plane has charter on the MR but you are flying back as a private flight and can therefore do SE NVFR.
In the same way if I got out to the destination, restarted and found that an instrument required for charter but not private was busted I could still return to base (having made the appropriate notes on the MR and placards etc.)
You are confusing maintenance category with category of flight which is what is referred to when we talk about instrument requirements for VFR/IFR Charter v Private, as well as night flight.