I've forked a repo at GitHub for OpenCart, and it contains several branches
master
development-feature-profiles
v1.5.5.1
v1.5.5.2
v1.5.6
v1.5.6.1
The current master branch has all the changes in it for the upcoming version 2.0.
I've created my own branch, based on the master branch, let's call it:
development-2
It has a bunch of changes I've made to the core files etc. I'm not interested in doing a pull-request to opencart for these changes, or more accurately, they're not interested in merging my changes, so that's fine.
I'm leaving the master branch as is and pulling their updates into it.
My question is, how can I merge the new changes from the master that come as they continue to update the opencart/opencart repo that I've forked into my development branch, without overwriting my changes?
I assume that I have to create some sort of diff and patch but I'm unclear on how and I can't fine any instructions online.