Thanks for the help, I tried out your program, now I'm trying to load the project.script into the bundle modder, but it shows an error. Something with wrong format.

Open project.script in something like notepad and paste the contents here.
Open the mod folder and check that song.stream is inside there and that it's not 0kb. After that, open script.script in something like notepad and paste the contents of that here as well.

Okay, project.script:
@Name Song mod
@Author x
@Description Replaces x with x.
@Version 1.15

;Files included in this project
soundbanks/music.bnk : mod\script.script
soundbanks/streamed/music/668133142.stream : mod\song.stream

The song.stream is not in the mod folder, it's in the GUI's folder, and it's not 0kb.
script.script (only file in the mod folder):
Replace : AB AA AA AA 0E 87 ED 40 : 00 00 00 00 40 F4 E7 40

Replace : A6 AA AA AA 0E 87 ED 40 : 00 00 00 00 40 F4 E7 40

Tried to put the .stream into the mod folder and rename it to song.stream, but got the same error when I try to load it.

They look fine, I know if the file is missing it says "Replacement file does not exist. Line x" but I've never seen anything to do with a wrong format.

No matter, just add the files to a mod manually I guess.

Create Mod tab

Bundle File Name: soundbanks/music.bnk
Replacement File: script.script file
Add Replacement To Mod
Bundle File Name: soundbanks/streamed/music/668133142.stream
Replacement File: song.stream
Add Replacement To Mod

Fill in the name, author and description then Create Mod: http://puu.sh/k0qXu/d0473f1177.png

Thanks! It works! Not the perfect loop, but better to have 0.2-0.5s nothing than 11s nothing between tracks :)