Hello! I had an idea to add external hardware to my 3d printer.

Hello!
I had an idea to add external hardware to my 3d printer.
I watched few videos online, and also a lot of videos about LEDs for the printer.
I am using the Tevo Tarantule, and the control board is ramps mks 1.4.
I know the board is a mix of arduino mega, stepper drivers, and the ramps shield, and I would like to get an access to the arduino mega pins. it will be very nice to find unused pins, and use them by editing some of the Marlin firmware.
I found out that there is a port on the board called “AUX-1”, and maybe I will be able to use it for my ideas.
Is it possible to do something like that?! and if not, is there any other way to do it, without the aux port?

BTW, I will probably need only 3 pins, and that will be enough for me, but more of them will be also great!