I'll try this out, thanks.
When you talk about the IDs "0B" and "30", you're talking about the name of the files or the coding?
Because the Slot files are named like that, but said numbers are also seen in the images.
EDIT: The game still doesn't load my Bowser clone. The game freezes as soon as I select a Stage.
You can see the IDs I'm talking about in this image:
Fighter Data Chart, Giga Bowser only have a Fighter (30) and a Slot (2C) Config files, the SlotConfig use the Fighter ID to determine what character it will transform if the character can do it. You don't have to worry when cloning because they all use the same ID for the 4 types of config files unless you use a Boss Slot.
And for your problem if you're using the correct rel (ft_koopa-alone BX v1.1.rel) and it have the right ID in the rel and your game is having a soft freeze then you probably forgot a file, check if you have all the files that appear in the BrawlEx Config Utility, although some of them aren't really needed like the Fit_Spy & The Fit_Dark, so it could be the files for the Kirby hat which you need to select in the Kirby option as "None" to make the game to doesn't search for this files.