It has come to my attention that not all stages work with STASH (even when no errors come up through it). When these stages, namely STGEMBLEM_00.PAC (the first part of Castle Siege), are loaded, they freeze. Here is how to fix it.
Take the edited stage and original stage and put them both in a hex editor. For this demo, I used Cygnus free hex editor, but any should do. I also used STGEMBLEM_00.PAC as my stage.
Go to the original stage and locate the first ARC in the ASCII text. Highlight that chunk of data until you get to the second ARC (which should give you 60 bytes), and then copy it.
Go to the edited stage and paste the data right before the ARC (the only one there).
Now it will look exactly the same on both pac's for the beginning.
Now scroll all the way to the end of each pac.
On the edited one, delete the duplicate data (use the unedited pac as a model) and then you are set. (you should be deleting 60 bytes of data)
Now replace in Brawl and play as normal
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