This isn't really a question as much as a comment ;o)

Live site is zc 1.5.5e recently update to f. Responsive Sheffield Blue 2.0, many mods. In preparation for eventual aging out of my template I built two test sites first. One updating and testing my live site files with live site db, and the other with a clean install of zc 1.5.5f and a clone responsive_classic template.

On the latter, I installed Canada Post, ckEditor, OPC 5.0, EZPop4 and Colorbox 1.2.2 followed later by IH5, SbyA most recent, and Attribute Replace Main Image.

Following the instructions on the Misc tab of IH5 I used the IH5 version of incl/modules/YOUR TEMP/additional images.php instead of Colorbox v. To my great surprise, everything worked nicely together with very little fiddling. Attribute images swapped, stock counted and adjusted, lightbox with additional images fully functional.

So next, I took the test site copy of my live site and tried to replicate this success, beginning by cloning a responsive_classic template. I didn't remove Responsive Sheffiled Blue. While it may be easier just to make my virgin site into my livesite I have great fear of losing my google rankings.

I ran into some snags. Biggest difference I can think of - non-template files merged as part of RSB template package or other mods added over the years. And perhaps relevant, Colorbox and IH4 were both resident on the RSB test site. I updated them to newest versions before adding SbyA, Attribute Image replace Main Image mods.

On my sample product I hit a snag with Attribute Images replace Main Image in both clone responsive and RSB - images wouldn't replace. Hit partial snag with SbyA - radio buttons for attribute showed but one button insisted on being default (not set that way) and the stock was being counted but didn't show (like it I try to add more than available to cart). Strangely, everything worked if I switched to Classic Green or Responsive Classic. My clone Responsive worked perfectly in the clean install test site, but not in the reworked test site.

I Beyond Compared everything to death, and eventually arrived at this solution:

Removing completely includes/YOUR TEMP/templates/tpl_modules_attributes and includes/modules/YOUR TEMP/main_product_image from both my RSB and clone Resp Classic folders rendered everything fully functional. Those files are both present in my clean test site and work fine.

I have no idea why, and I post this only in the event that it means something to anyone else ;o) I flipped a coin where to post this as it involves interplay of many mods, but I didn't want to cross post.