Short answer: If you follow the rules above, WWE 2k14 wont get confused reading different save files because it will only search for a save file with its own title id that's inside the save folder with the title id it's been assigned to.
Long answer:
bare with me:
You create a wwe 2k14 backup on your pc. It's copy of the wwe 2k14 iso you extracted from your wwe 2k14 disk.
You then extract that iso. Now that you have the wwe 2k14 directory, located inside is the xex file.
You follow the directions above to change the title id in the xex file.
You place wwe 2k14 into you RGH'd HDD.
You run the xex file that contains a modified title id.
If all above is done correctly you will not have any problems. The xbox will create a save pertaining to the new title id. It will not mix with wrestling legends. Doesn't matter if an exact copy of wwe 2k14, if the title id's are not the same, both saves are foreign to each other. WWE 2K14 will not scub your HDD's directory for save files that are the same format as itself. WWE 2K14 (or any game as a matter of fact) never really needs to access the files from other saves located in other title id's. There are a few exceptions of course, like how mass effect 2 can pick up your save from ME1. Or how skate 3 gives you a bonus item if it detects a skate 3 demo save. Other save files can be read by games as long as its deliberately programmed to do so. WWE 2k14 doesnt fall under this situation so you should be good.