Fixing permissions on a dual OSX setup

I recently did a fresh install of High Sierra on an SSD but wanted to use my old HDD to store my work files and a backup system in case I screw something up. Unfortunately I couldn't get my config or any bootflags to stick on the SSD EFI for some reason so I'm just using the HHD EFI to boot OSX on the SSD.

Well, I ran a couple of stupid sudo chown commands to get access to files on the HHD and now I can no longer boot into my backup system. Is there a way I can restore the permissions on my HDD install without affecting the permissions on my SSD install?

submitted by /u/Glaiwo
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