One great thing in the “Extend curve” (Type = line) tool is that it could either extend or reduce the length of a line. “Extend surface” in Rhino 6 also could do both of these operations. However, seems like “Extend by arc: keep radius” is incapable of reducing the length of an arc. Any chance to make it happen in a future release? 
Hello - I see that arcs only extend - looks like an oversight to me, I’ll get it on the pile - meantime, SubCrv should do the trick.
-Pascal
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Yes, that worked fine. Thanks for the quick response, Pascal!
Bobi
You got me pegged!
-Pascal
Sorry, that’s because my native language is not English. I accidentally pressed the “R” key, because it’s used to write the Bulgarian letter “Р” which looks exactly like the English letter “P” but is pronounced like “R”). I fixed it already. 
No worries! I think I know some who would say you got it right the first time… =)
-Pascal
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