I had to place my gpu back onto my motherboard after taking it out. And the only way to do it was unscrewing the whole mb and slightly tilting it, which also meant loosening the screws holding the cpu cooler.
It was only loosened for a few minutes at most and i hadn't picked it off the cpu itself.
Whilst i know that if i was to separate the parts from each other i'd have to reapply the paste, the heatsink was always laying on the cpu. It didn't break contact from the cpu but rather had a change in pressure between the 2 once i loosened the screws. This has the same effect on the thermal paste, is that it?
Just run some stress tests and see if temps spike higher than before during the same test (or is higher than you would expect with your CPU/cooler combo based on a web search if you haven't run stress tests before). If not, then you obviously do not need to do anything. I don't understand why I am the first to suggest this, given that it is going to (potentially) involve by far the least amount of effort and save you wasting expensive paste for no reason.