Option to set a file association only as "Open with ..." option

brasmusson  The traditional app that you capture has several ways to set up the scenario you desire when deploying via MSI or Setup.exe. Those scenarios include setting the .fta using the openwithlist,  openwithprogid, or even a Shell "alternate verb" entry for the particular type without modifying the default value of the .fta key.  Another method involves registration via the "App Paths" key.

It is my experience however, that the packaging tool does not properly capture any of these situations, usually resulting in the app becoming the default upon install or being ignored altogether. 

Manual manipulation of the manifest might be able to produce a solution -- I'm not sure -- but certainly your uap3:FileTypeAssociation element would require the uap:SupportedFileTypes sub-element to have a chance to associate at all.