So at the moment CDG-DUB is still operating? If so then you options hinge around that flight operating, so you can't get rid of that at the moment. You somehow need a CDG-LAX route, which can be via London or using AA via DUB or something similar. For the return as things stand you can drop LHR-CDG and get a small refund on that component.

Generally speaking I would advocate you only now make a change when you are forced by circumstances, such as the aircraft being at risk of sell-out (somewhat unlikely at the moment), otherwise stick to changes that you are 99% sure will work for you. And no "maybe" arrangements made in haste. If you instantly rebook you instantly lock yourself in, at least potentially into the new arrangements at the airline's charity, as opposed to what works best for you. However. There may be an argument to make this CDG-LHR-LAX/SAN-LHR now, since there will be some chance of CDG-LHR being dropped and thus you are in a position to take advantage of that, which you can't do if still booked on CDG-DUB-LAX. However if that CDG-LHR sticks, then you need to travel from CDG.

You could simply FTV the lot and rebook from fresh, but I would only do that about a month from departure and only if you were pretty sure CDG wasn't possible.