Hi,
this sounds doable and should work like you expect it. However i see a couple of downsides.
For once you will have two separate entries in /Aif/err for each messsage which could be dificult to connect during support issues. Furthermore you would have 2 points of failure so you allways would have to check both parts to make sure a message went through ok.
Have you taken a look at interface variants ? I could imagine a scenario where you create an interface for all "base" structure mappings and so on and a variant for each of your outbound interface demands in which you can handle the specifics.
Given a proper keyfield configuration you should then be able to have just one interface in /aif/err that presents messages grouped by the topic
Kind Regards
David Rittinghaus