Locking control points to the edge of a random shaped flat surface

When I have a random shaped flat surface and I rebuild , I get many control points outside the surface edge.
When I select points close to the edge on the inside and use gumball to raise them in the Z direction it lifts the surface edge also making it near impossible to connect an adjacent surface edge to. How can I lock the surface edge in the flat position while allowing the parts I have selected to move? I tried shrinking and shrinking edge but I still have the overhanging points outside the surface edge. I know there is a simple thing I am doing wrong…! Thank you greatly in advance for any advice

Not really.
NURBS surfaces are always rectangular. When you shrink a surface, it gets as close to the trim curve (your edge) as possible, but it will remain rectangular.

Short of putting in extra rows of control points close to the underlying edge, there is no way of “locking” a trimmed edge.

I use SetPt afterwards to bring the control points adjacent to the edge back to a planar perimeter surface. This still leaves small deformations along the edge. Then I run contour and get multiple section curves. I use SoftEditCrv with control points turned on to snap the curve ends precisely back to my desired level. Then Networksrf or similar to regenerate the surface. This allows me to limit the distance tolerated for changes to the edits to the original control point z heights adjustments.

thanks buddy. Doing my head in!

Epic! Thanks Abraham, certainly a comprehensive solution. I usually use for laser and CNC but this is a simple architectural render so not critical but seriously weird that there isn’t a way of locking them down on that plane… Thanks for the your solutions buddy