Many thanks to Trenloe and Nickademus for this very useful extension. As others have pointed out, it served as a great example of how to interact with the FG code infrastructure and taught me a great deal.
Continuing the conversation, I would like to suggest that even though players can remove effects via the combat tracker that is not necessarily optimal. You most likely entered an effect via your actions tab and you should be able to remove it as needed via the same location. While perhaps a minor efficiency gain keeping the REMOVE effect in the actions tab, it is a larger organizational enhancement.
Second, my requirement for this feature came about from a side conversation with Zacchaeus concerning a potential bug with 'once per modifier' timing. The REMOVE feature is (almost) exactly what I needed to overcome that deficiency. While correcting the behavior of the 'once per modifier' timing issue would be the closer to the ideal situation, your extension makes the sequence simple. (FYI, the issue is that while all of the effects are popped from an effect using 'once per modifier' timing as expected, any tag associated with the effect remains behind). (FWIW, the ideal for my current problem would be to allow the Weapon Meta dialog use 'per weapon' instead of on the Weapons group.)
Thirdly, in order to make my preferred sequence work (in light of the deficiency noted), I had to make a minor tweak to the remove_effect_tag.lua script provided in the extension. This might be usable by others but I will ask how best to disseminate since I am VERY new to this platform. Essentially, the REMOVE effect as enhanced does not have to be encoded exactly as the effect is written, one need only supply the tag. (It has a few protection so removing tags like 'a' doesn't remove 'aa' and so on.)
Lastly, the next logical enhancement that I plan to undertake is to make REMOVE work with multiple tags. However, I suspect that this will need to be an effect all its own (e.g., REMOVETAGS: <tag1>, <tag2>, ...) in order to avoid fundamental parsing/pattern matching problems with the original feature. Any and all suggestions are greatly appreciated.
Thank you all for the excellent information!
P.S. the use of REMOVE: prone is awesome, too!