kamal, Welcome. We have a handful or so of plug-in authors who are less than daily contributors here, so a knowledgable response may take a day or two.
In the meantime, I'll babble on with a less than knowledgable response:
I believe the Modules folder is a holdover/backwards compatibility feature from Lr 1.x. which is not completely forward compatible with and the Lr 2.x plug-in manager. I've seen plug-in authors complain of the impossibility of 'Managing' a plug-in, which is physically stored in the Modules folder.
(Edit: I note that Rob Sylvan gives a much better description of this, in the other thread in which you're participating.)
Nonetheless, I will cite the example of Tim Armes' LR/Mogrify (the version intended for Lr 1.x), which I've just been fiddling with, and it clearly installs as enabled, and uninstalls, simply by placing/removing the plugin package in the Modules folder, so your desired result must be possible, at present. Who knows about future compatability of that apparently deprecated method?
I know this isn't contributing much, but I did want you to know that your thread has been seen, and to check back for updates.
