External USB on Pi400

[mallaard]

Hello, I'm fairly new to Recalbox, it's installed on an SD Card in the PI400 inside of my MAME cabinet. Recently I decided to connect an external harddrive to expand storage, and so I formatted it to the current Recalbox image and it created all the folders and everything on the harddrive.

My question is, since the image on the SD card is programmed with a slight overclock, do I need to apply one to the setup on the USB drive as well, or will the one on the SD card still function? Also, does the SD card itself still need to have Recalbox installed in order for the Recalbox-formatted harddrive to function, or is the harddrive basically its own installation, meaning I could possibly try something new on the SD card like Retropie or something?

Thanks in advance for any feedback!