Change the modifier keys on the right side without changing the left ones I have a new keyboard connected to my macbook (high sierra) that I'm currently adjusting, and I would prefer if the first key to the right of the spacebar was an option key and the next a right ctrl key. I know that the modifier keys can be changed in System Preferences > Keyboard > Modifier keys, but that does not let you change the left and right sides independently: the two keys closest to the spacebar stay the same kind no matter which kind you choose, and I want the first key to the left of the spacebar to remain a command key.

I have used Ukelele before to modify the layout of the rest of the keyboard, but as far as I know,  you can't change the modifier keys with it.

Is there any way to make this custimization? It can't be a limitation to the hardware, right..?
In setting you can't do that, but with the karabiner program you can. You'll find karabiner here: https://pqrs.org/osx/karabiner/.

Install it and open Karabiner event view. Press the key you would like to change and then click 'Add ... to Karabiner elements' where '...' is the name of the key you want to change. In the program that pops up, select the event that you want to remap the key to from the left drop down. 

Note: This does not work on all keyboards because not all keyboards does send the difference between left and right key. You can tell if your keyboard does in Karabiner event view under the name section after clicking a key. In such case, there's a hardware limitation.