Shorten surface - negative extension - extrapolation

I would like to shorten a surface by his edge; in other software (like Alias) I use EXTEND SURF command with negative parameter

If the edge is untrimmed, you can split with an isocurve. If not, you can offset the edge on surface and trim with that.

Yes, but the result will be a trimmed surface, not the same result of an extension with poles at the end of the surface; with this workaround I can’t align the surface with another one, i must use SHRINK also

Well, if the surface was untrimmed before, then splitting with an isocurve and running shrink on it will make it untrimmed again. Or is that what you are saying?

Yes. It’s a workaround instead put minus ahead the extension lenght

Hi Daniele - Rhino V6 will accept a negative number and allow interactive ‘extension’ in both directions.