Well, it's functionally possible to support plugin deactivation (not sure about actually removing the plugin altogether), but most plugins probably don't do so unless they have some reason to support it. You should be able to write an override to the plugin and insert code that would allow you to activate/deactivate its functionality. Depends on the specific plugin of course, but if the plugin is well-written it should be overrideable.
My general approach would be something like:
Ext.override(Ext.ux.plugins.SomePlugin, {
isActive: true,
doSomething: function(){
if(this.isActive){
// copy orig doSomething
}
}
});
Then you could simply set pluginInstance.isActive = true/false
as needed. Note that this is simplistic -- your plugin might take a lot more work to override effectively. But this approach would be a good place to start.
Or you could maybe get fancy and use createInterceptor
functions on the plugin to do something similar without duplicating code.