When this client moved to another home, the valance was too long. To remedy this problem I removed the valance from the board, dis-assembled the ends and removed fabric from each end. I re-cut the end sections to match the center and re-attached. Good as new.
This treatment was a bit more difficult. This was made to order from another state and non returnable. When it arrived, it was 3 inches too narrow for the window. Again, dis-assembly. I'll spare you the details of the wood-working. But I was able to re-build this treatment (to fit perfectly) and save it for the client. And you would never know it was altered.