Overwriting an existing UDA in designer and Manage User Defined Actions section
Since we can overwrite an existing workflow by importing and then saving over an existing workflow, I propose the same functionality can be applied to designing a UDA.
For UDAs that cannot be promoted to farm level for whatever reason, a UDA would need to be imported into whatever sites are going to be using it. In my situation, we develop a UDA in a site designed for testing, and when our changes are ready to be deployed we'd then have to replicate those changes into the UDAs being deployed in production.
From my understanding, if we were even going to use a farm-level UDA, it must first be exported, modified, imported back at site level, then promoted (after the current farm UDA is deleted). This process is more involved than it honestly needs to be.
It would be efficient to just be able to overwrite an existing UDA, but current behavior duplicates the UDA instead. I propose that there be a feature to save over an existing UDA in the same manner that you can overwrite an existing workflow when saving (the "Overwrite existing version" check when saving a workflow).