Does an amended shortcut clearance change the clearance limit?
I assume that this question is about the US, based on your examples. 

No, it doesn't change the clearance limit. For some reason I could only find the documentation in the ATC orders, not the AIM. Section 4-2-5 of the orders says:


  
  Issue a clearance “direct” to a point on the previously issued route.
  
  
  PHRASEOLOGY−
  CLEARED DIRECT (fix,waypoint).
  Or
  CLEARED DIRECT (destination) AIRPORT.  
  
  NOTE− Clearances authorizing “direct” to a
  point on a previously issued route do not require the phrase “rest of
  route unchanged.” However, it must be understood where the previously
  cleared route is resumed. When necessary, “rest of route unchanged”
  may be used to clarify routing.


If the clearance limit changes, the controller will usually give you a completely new clearance to copy.