What you wanna do to model swap a second or third model in the tag its very simple. You have to search up:
Example of the character we're using:
609 (Tag Fusing Vegito
You need to search up
609;11000609 (Goku side)
609;12000609 (Vegito)
(D-Word)
Now to get these models you have to look for either 11000609 or 12000609. There will be multiple of these shown when you've searched it up but you need to select the second lowest of 11000609 or 12000609 that has been searched and click "Go To" on it and the first ODD Number or Purple Value will be the 2nd or 3rd characters model that you've searched for. Its not the second purple value like on normal units. Its the first value