Hello Noseemee70
I suppose that you could exchange the TGV ticket to arrive earlier in Basel.
If you could buy an exchangeable (semi flex) TGV ticket from Paris to Basel and a non-exchangeable non-refundable ticket from Basel to Interlaken in the same transaction, it is not logical. In this case, I suggest to ask the SNCF customer service to know why it was possible.
If you bought the tickets in two separate transactions, you have two contracts with their own conditions.
Kind regards
Danhiel