Hi kahuna - it's normal that you will not see any change of appearance after ShrinkTrimmedSrf, unless you are showing surface control points.

The way trimmed NURBS surfaces work is there is an "underlying surface" that then has trim curves on it which mark holes and cut away spots.

It is possible for that "underlying surface" to be quite a bit larger than the current active area. ShrinkTrimmedSrf will shrink down the underlying surface so it is only as big as needed to contain the trim boundaries.

Since you don't normally see the full underlying surface, any changes to it outside of the trim boundaries can also not be visually apparent. But when you turn on surface control points those are shown on the full underlying surface.

- Michael