Unfortunately, unless the Plugin has specifically coded the ability to disable itself (which would be very kind of them) - you cannot disable a Plugin in game.
The way Plugins work is that they re-write and modify the game-code at launch (Plugins are ran like programs, its their responsibility to modify the game-code to add in their behaviour). This modification cannot be undone without knowing what the Plugin changes and without having an original reference to the unmodified version of the game-code.
Even if the Plugin coded a way to disable itself (seriously I like the sound of this, I think Plugins should start doing this) then it would still leave residual logic behind, it's not going to get 100% cleaned up and removed. Global variables will stick around - unless the Plugin deletes them, but this may cause problems if other Plugins depend on these variables. Save data variables will also stick around.