if i change my rear derailleur should i change my chains too?
no, those are not really related.
You need to change your chain if it becomes too long.
And if you wait too long you might need to change the cassette also.
If you’re swapping your derailleur for the same model, no.
If it has a longer or shorter cage than you might need to.
Plastic jockey wheels are so soft compared to the chain it’s not going to affect chain wear.
I wouldn’t use a new chain, but have transferred the old jockey wheels to the new derailleur. so that everything is in a similar state of wear then put the new jockey wheels back on when I replace the chain.
I think this only applies if the longer cage is needed because there is also a larger cassette.
One of the methods to set the chain length even ignores the derailleur completely: you put the chain around largest sprocket / large chainring, not going through the derailleur and then add 2 links, or 3 if needed to make the ends connect.
This is where the “might” factors in.
Without knowing what OP is doing we can’t know for sure. Moving from a short cage to a long cage with a triple on the front you may have some issues with chain length. Less likely on a 1x.or even 2x.