If you rotate gear often, don’t use them (1260 or Q45T) yet because they aren’t cheap (unless they are not cheap for you). Just wait until you settle then give them a try. However, like me and many others here, your curiosity got over you and want to try them? fully apply them in a very thin layer as possible between 2 metal surfaces of the connectors. Avoid gaps.
If removed or disrupted those bonds, re-coat again in a very thin layer.
Yes, you can apply Q45T over 1260 and they can still go together. However, wipe off 1260 before applying Q45T will give you more accurate of Q45T’s sounding signature. In my opinion, the Q45T is better than 1260. It gives me more music so I personally wipe off 1260.
Great luck and have fun with it.