Best way I find is to use the WeMade Image Library Editor... sometimes you cant open wil's using it because it doesnt support wil type 2.
But if you use hh8 to export and import them all it will turn them into wil type 1 allowing you to open them in the WeMade editor.
With the WeMade editor you can just highlight the items you want to copy over into your new wil file. I personally think this is the quickest way it can ever be done.
I don't think anyone will disagree with me on this one if they use this method or even try it.