If what plugin is enabled?
If you have to go to the trouble of enabling/disabling plugins for different builds, then you may as well just do a Control Switches at the start of the game.
I also wouldn't do it via $gameSwitches anyway, because that's only available after a new game is started, and not immediately on loading (which is probably why yours isn't working), and it would be saved with the save file. If a player started playing on one device, then saved and resumed on another, that switch would be incorrect.
It would be better for you to explain why you want to do this, so we can give you a more appropriate way to do it. rpg_core.js, for example, has logic built into the different functions that depend on the device. It doesn't save the info anywhere. It looks it up when it needs to know.