Maybe there is (I can not test it), but you shouldn't.
Changes are that your script won't run on a 9.51 load generator. For
example because it is using functions not jet available in the older
version.
The right order is: first upgrade PC and then Vugen.
You could try to open your script in Vugen version 9.51, verify that
is still works and then upload it to PC.
André