Yes, if spare parts are not available, repairing the pins should not be too difficult.
As for the difficulty in uncoupling the cars, my Kato train sets usually come with instructions how to connect and disconnect them, and also with spare parts list. What kind of documentation came with your set?
I have several bullet-train type sets from Kato and none of those are especially hard-to-uncouple. While the coupling is usually done by butting the cars together, uncoupling often involves shifting the cars vertically to release the latch, or bending the coupled cars (as if they were traveling on a sharp curve) until they separate.
Maybe someone else here owns that set and knows a non-destructive uncoupling process. I was also going to ask you to maybe post a photo of the couplers, but you need to have at least 25 posts under your belt to be allowed photo uploads.
