When in the OmegaT configuration "Allow source equal to target" is off, it is not easy to insert an identical translation (source=target) in the TMX. However, when you set "Allow source equal to target" on, I am getting a lot of user faults because one click in a translation is sufficient to add it to the TMX. And it is a global setting for all projects.
In our projects, we often have hyperlinks as separate segments to be translated, but they often remain the same when the hyperlink is not-translation dependent.
My preferred approach would be to have an option in the Edit menu: Register identical translation with a shortcut key.
This would then be the way to work: No allow source equal target, unless you have pressed the shortcut key on the segment itself. In that case it is added.