Pretty sure I already know the answer, but am just checking.

Do the Propellers have a max number of flights ? (replace after x number of flights) or is it only if they are damaged in some way ?

I bought extra propellers just incase but I`m still using the first set it arrived with, and am noticing a change in the noise they generate while flying, it isnt a bad noise, its just changed.
I guess its probably just the different conditions in the air but am just checking.

Cheers

As far as i know and have read, you probably only need to replace if damaged.  Thats just my thought, probably worth a response from the very knowledgable @DJI KEN or other DJI staff member on the forum with regards to this though.

If they show any damage bin them, but other than that you can use them as long as you like, some people like to change them after a period of time and that's ok to, in the scheme of things they are inexpensive.  Good luck.

We recommend that they are changed around 200 flights.
If the propellers are scratched or damaged, please replace it.