I have installed it and it was fun to use the omod, the problem is that I'm not able to remove the mmm plugin for knights of the nine. I don't need it, but trying to delete is impossible

why not just go into your oblivion data folder and delete it?

do you think I won't mess up with the omod itself?

no it will not, afaik. just be sure mto deactivate the plugin before you do

And that is also another reason to use Wrye Bash's BAIN - that will allow you to add/remove esps with a few simple clicks, and all it takes for MMM is some folder modification to make it work with BAIN...