Hi SebKaine,

re:
> - untrim the patch
> - recreate a new projection curves by rebuilding the actual contour curves but without the font
> - then reproject the reconstructed curves and trim again ?

Yes, but you can trim with the edges of the neighboring faces, you don't need to do a separate projection step.

So after separating out the face, select this trim boundary (select 1 edge then Ctrl+a):



Delete and you'll have the underlying surface:



Select it and run Edit > Trim, and select the neighboring edges as the cutting objects:



Don't forget this little edge here:



Inside the Trim command select these pieces to discard:



Result:



- Michael