My 2 blue-tit nesting boxes are both full of earwigs. If I clean them out now I guess they'll just move back in again: maybe I should do it at the end of the winter, or won't the birds mind?
I don't think the birds will mnid (maybe they will eat them!).
I would clean the boxes out now with boiling water anyway in preparation for the spring.
I once noticed that one of my peanut feeders wasn't being visited and when I investigated it I found it was full of earwigs between the peanuts. I emptied it all out, cleaned and refilled it and the birds came back to feed from it.
It definitely put my visiting birds off, so if it was me I would get rid of them straight away before they breed to even greater numbers.
Earwigs in bird boxes are not a problem as blue tits may well make a midnight snack out of them! Earwigs pose no threat to the roosting or nesting birds so if they do venture back in there after you have done the autumn clean out, don't worry!
Generally October is the best time to clean the box out as it will not be in use apart from as a roost site if you are lucky. It is best to get the box cleaned and returned to its normal place well before the birds start prospecting again for next years site, many birds start doing this in winter so stick to nest box cleaning in autumn as it is less likely to disturb them.