I uninstalled/deleted a system-privileged app (from /system/priv-app). How can I reinstall it?

I uninstalled the DocumentsUI only to know it wasn't "just" a file manager. My /system/priv-app/DocumentsUI is empty. Putting any 3rd-party DocumentsUI.apk in it results in a bootloop. I have a custom ROM (AOSP Extended). Flashing the /system again would fix the problem, I think. Just want to make sure if this will make the condition worse, or am I going alright?