In most countries, there is no restriction on which side you sit if you are not a qualified pilot. However, I understand that in Germany, the Commander must occupy the designated seat.
There may be very good reasons why you should not occupy the LHS, but those would be aircraft specific (e.g. some aircraft may not have RHS foot brakes, or the fuel selector may be difficult to reach from the RHS).
But, in the scenario you describe, you would only be able to log 'passenger flying'.