Hi lansti,
I'm afraid that's not possible. FTA's only support a single application for a particular file extension, and although you could maybe use some conditions to decide which application that should be, that choice then applies until you refresh the FTA configuration. That is, there is no way with UEM to make this sufficiently dynamic.
I don't think there's an appealing solution for this anyway, I'm afraid... The best I can come up with is to create a specific "version selector" application and associate that with the .edlp extension. That application could then ask the user which web site they downloaded the file from, and launch the corresponding version of the application.