Is there any way to change flag? For example when you by mistake past ID of wrong post in reason duplicate/inferior or any other mistake.

Nope, there isn't a way, but if you find a mistake simply leave a comment, we usually check them if the flag doesn't make sense.

I will try to remember for future, but I think that posibility to delete your own flag (even time limited) in case of mistake would be nice feature.

Thanks for fast answer.