I'm looking at upgrading from Zen Cart 1.3.8a to 1.3.9c. I need to add all the code for the Stock By Attributes add-on.

QUESTIONS

1. Is adding the code by hand pretty straightforward?
Merging a few of the files into 1.3.9c was initially intimidating for me, as some files have been changed big time (esp orders.php and order.php). What made it MUCH easier for me was to first look at the SBA file against the zc 1.3.8a file where it was very evident where exactly the few SBA modifications were. Then I went back to comparing the SBA vs zc 1.3.9c file knowing which things to ignore as new core changes.

On top of that, most of the SBA code is clearly identified in blocks.

I don't know/write code, and I found it fairly straight forward.