I'm racking my brain trying to think of a way, but I'm not sure how you'd get an interior to fully move to a new esp. That sounds like any scripts, unique ID's and activators would have to be converted over too.
I have an Idea but I don't want to fry my own mod if it backfires. I thought of opening the file in FNVEdit (with all of it's masters, etc.) and removing the navmesh from the world cell in your mod, opening back up in Geck and seeing if the Fallout.ESM replaces the area with the games default navmesh map.
I know that the only really hard part of exterior navmeshing is getting the intersecting X lines to match up to turn green on finalization of the cell, so maybe this would restore the integrity of the default navmesh map so you can possibly start again?
If I ever accidentally delete exterior vanilla navmesh triangles, I just rebuild them to form fit the terrain and match the existing vertices that are pre-placed. I've never ran into a ctd problem caused from my own edits as long as it all links when finalized, and my last released house mod actually utilized an exterior cell w/o any interior cells, and I've received no complaints or problems with the edits I was forced to do to the vanilla navmesh.
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