Dynamic Apparel System

Pardon me if this question has already been asked.

Is it possible to implement a system into Pokémon Essentials that allows players to customize their attire, similar to that of Pokémon X and Y into RPG Maker XP? If so, how would it be done? In addition to being able to customize their player with different outfits, I need to know if it's possible to make all changes to the player's appearance take affect not just in the overworld, but also for in-battle sprites (right before the trainer throws the pokéball), as well as the Vs. Bar sprites right before fighting notably stronger opponents (such as the Elite 4 or the Champion).

You mean player outfits? Yes, those are a thing.

The only game I know of were you can customise your trainer fully like x and y is Pokemon insurgence. Which I think is done by overlaying clothing sprites over initial the pc sprite. That's the theory behind it I don't have a clue how to go about implementing it though.

Like Maruno implied, an outfit system already exists within Essentials. It's essentially identical to the forms system used for Pokemon like Kyurem, Giratina, etc. - just applied to humans instead of Pokemon.

Now, how you take advantage of this is up to you. Do you buy clothing items in stores? Do you force the player to change outfits every time they beat a gym? Etc.