I tried using a different program (can’t remember the name) to replace icons for 2.3x runtimes, but it didn’t work either. Someone needs to update Icon Replacer, or even better, add a Choose Icon feature to Blender.
I had similar probs but I found a free/shareware program called “installer 2go”(do a google)that enables you to change icons as well as zipping the daylights out of the file size.
You may need to change the icons resolution and
size to work properly