Inset while keeping part of the shape intact I would like to know if it is possible to use the inset function while keeping part of the shape intact.



Circled is the part I don't want insetted, and I tried to show a global idea of what's the result I want to get with this. This knife/sword edge is one use case I can think of, but that would also be useful when insetting at the border of a mirrored object, to inset the global shape instead of just the half you're modifying.
One simple way is to temporarily extrude the shape and inset part of extrusion which will create edges on the boundary. So instead of a plane:


You use the same form but extruded (or just extrude one edge where you need edges to touch the boundary)


Then select top faces plus one on the side and run Inset:


Dissolve unnecessary edges on the side as required (or delete bottom vertices to get rid of extrusion), note that dissolving might create Ngons which are better to avoid.