He wants to know how to hex edit, not use Stage Switcher.
Open up the .rel you want to convert in HxD.
Look for this string of hex: 38 A5 00 00 38 80 00 01, then replace 01 -- the ID of Battlefield -- with Hanenbow's, which is 25.
So, your string should be 38 A5 00 00 38 80 00 25.
Save this file as "st_plankton.rel", and you're done.
Go
here for more info.
I don't know anything about hexing characters; sorry.