WOW!! You are a genius!!! The short answer for anyone else out there with this problem is thus:
To have a specific ruleset tab displayed on CMMOS 4.05, you must have the Infoxxx.txt file included in the RuleSetxxx folder in your GEM Software Productions/CM Mod Option Selector/CMBO folder, where xxx is the ruleset number (001,002, etc.) that you want. Having this file there is what creates the tab for the ruleset. Just copy this file from Ruleset001 (which is one of the CMHQ ones that does show up in 4.05), rename it from Info001.txt to Info241.txt (for example, to create the tab for Ruleset241 - Darkight's 21st Army Group), change the Ruleset Name within the file to what you want to appear on the tab and Save. Voila! If you've manually created the RuleSet241 folder (staying with the same example) correctly in your GEM Software Productions/CM Mod Option Selector/CMBO folder, and unzipped everything from Mike T's zipped rulesets on this site into that folder, then suddenly you will now have the new ruleset in CMMOS 4.05, with all its activated and inactive icons nicely displayed.
Thanks Philippe! It's always great when the solution is something so small and simple!!