This is NOT for a simple drive letter change (For just the drive letter I'll just use the disk management method)
This is NOT meant for ROMS contained in a single folder (For this I'll just use the right click option)
This is a fix primarily for game paths with subfolders:
Notepad ++ is the best method for editing "new game paths" for an entire collection of games with a click of a button:
For example changing the "drive letter" or even new folders all together with "new paths"
It needs to done for each system/platform "separately" though
Find your system xml file in Data\Platforms (e.g. 3DS.xml)
In the platform xml, each game path will start with <ApplicationPath>
Press CTRL+F for find options, switch to the Replace tab; tab will do all the work for you
In the Find what: field enter the current path (e.g. "..\GAMES\3DS")
Let's say you moved all your roms to a different folder or drive location
In the Replace with: field enter the new path
ex. New path: (D:\NEWPATH\3DS)
ex. New drive: (E:\NEWDRIVE\3DS)
Click Replace All and done! save; exit launchbox and relaunch app.
You should be able to play every single rom/game in your platform now; rinse and repeat as needed for all other platforms