Mark1234,
There is no right hand seat endorsement. There is a right hand seat approval, but even this is only an in-house thing ie not a CASA approval.
As previously stated by a few, unless the AOM/AFM states otherwise, you can sit either side you want (but unless intructed in the right hand seat I would not recomment it).
It is your log book and you can fill it out anyway you wish. If you only intend to remain a PPL and you have one of those ATC logbooks, you may wish to use the Specialist/Instructor column to record your trips away. Provided you put the times in those coluns only, you could add them up and it wont mean jack to anyone else but you. After all it wont be added to your total aeronautical experience. You could even have a differant logbook dedicated to the flights you refer to only. Just as you rightfully stated there is nothing mythical about the RHS, so it is the same with your logbook. It is a book with a log of your travels. Just dont fudge or incorrectly log your time.
As for manipulating the controls from the right hand seat with a PPL buddy sitting next to you is something maybe CFI can ellaborate on. My understanding is that a PIC is the pilot responsible for the operation and safety of the flight. He doesn't have to fly the aircraft at all, and provided that only one person is logging time for the time that they are flying, you could go hour for hour or 10 mins for 10 mins or whatever you wish from whatever seat you wish.