I have made a working RPG Maker MV plugin for the Konami Code that you can activate at anytime during gameplay. Up, up, down, down, left, right, left, right, B, A (X, Z on keyboard). Free to use with any personal or commercial project with attribution.

Add to your project's js plugins folder. Activate with Plugin Manager. Select which switch you want it to turn on, using the parameters or by editing the code