Running games on USB (HDD)

[Dopy25]

I have read the directions on mounting a usb HDD (or other) and have been able to copy the whole file structure. I went and added ROMs. They copied to the SD card. I did not mean for this to happen. I forgot to stop rom service.
I have a few questions:

1. If I stop the rom service now, would I be able to delete the ROMs from the SD card somehow?
2. Would the file structure remain the same, or must I start over and finish by completing all the steps under "Manual Mount" on the "Running ROMs from a USB drive" page?
3. Do I need to complete the steps to configure fstab to automatically mount USB drive?
4. Must the HDD remain attached while powered, or if I disconnect or unmount, will it mess anything up?
5. Can this be configured on one pi and move with the SD, or must I mount it on the final device?

[Dopy25]

I figured it out.

Problem was I followed a tutorial somewhere that said to make a folder called retropie whereas the official instructions state to make a folder called retropie-mount.

"retropie" will in fact copy everything to the HDD, but it will also copy from the HDD to the SD.

"retropie-mount" seems to copy everything from the SD to the HDD but will not copy everything back to the SD.

"retropie-mount" is sufficient to mount the HDD and play games. I did not need to follow all the steps to manually mount the HDD as mine is going to be portable.