Alright, as not to take away the challenge here's how you would put Yoshi over Lucario.
1. Open up Lucario's Plug&Play rel in the module editor All the current Plug&Play rel's are
here2. Click the top branch (ft_lucario Plug&Play) and look at the box on the right
3. Where it says "Id" change 0x76 (Lucario's Module Id) to 0x5F (Yoshi's Module Id)
4. Expand the top branch and click "section[8]"
5. To the right you will see a button labeled "Memory Viewer" Click it.
6. Click the first box and change it from 00000021 (Lucario's Character Id) to 00000004 (Yoshi's Character Id)
7. Close the memory viewer and save
Note: You can ONLY edit the Plug&Play Modules