Okay, I'm going to take a stab at this, I hope I'm understanding you well.
The pattern has the following:
thin border (purple)
thin pieced green 1"
thin border (purple)
wide border (patterned)
Correct?
You are wondering if you could increase the two purple borders and the wide border, right?
Okay, assuming that's correct, here's my thoughts on the matter.
I think you could safely increase both thin purple borders, but not by more than a 1/2" or so until they started to look funny and dwarf the pieced border.
If you choose to increase the outer border, I think that would be fine, but I think at that point I would like to see something "interesting" in it. I'm thinking perhaps purple cornerstones and a 3" or so purple strip in the center of each border (not longways, kwim??). Or maybe green fourpatch cornerstones and a fancy contrasting thread border quilting design. I think that would look better than just adding a lot more width.
Hope that makes sense!
Isabel