UNTRIM Surface only one side

I have a surface that has a few trimmed sides. When I untrim one side of the surface, the whole surface gets untrimmed on all sides. How can I untrim only one side of the surface?

For Example, I would like to untrim only one edge in the following picture.

If the trim represents the outer border of a surface, Untrim will naturally remove the entire outer loop to get the untrimmed surface.

If you want to modify a specific area on the outer border, you might try ReplaceEdge - check the Help for options.