Copy & Paste in the right-click menu from the Folder Formats list is the way to do it... Not sure why it isn't working for you though.
Are they the same type of format (i.e. in the same group of the formats list)? (AFAIK they don't have to be but that might explain it.)
Have you edited the format after pasting over it to see if the settings actually changed? If the format changes in Preferences but doesn't seem to take effect then it may just mean you need to close your existing listers and re-open them to avoid cached formats being used instead. Or it could be content-type formats, or inherited columns are confusing matters. (Both are talked about in the Folder Formats FAQ if you need a refresher.)
While experimenting around a new idea came into my mind.
Wouldn't it be nice if you could link two folder formats to keep them identical?
Why would you want this?
Here is my reason: I store my media files on drive D: but have hardlinks for them in the My Documents folder for Music, Pictures, Videos and so on.
Basically they are the same but for Windows and DOpus these are still separate places. This is why I wanted to copy a folder format. But now I have two formats for the same files/folders