Wow I didn't remember I have said this. You're lucky I saw your post
I know replace crashes. Or used to crash at least. I don't know how you're are inserting the object but it shouldn't crash. What I'll say now is not about the newest version of brawlbox, so there might be easier ways I'm not aware of.
Right clicking the model should have an option called "Import new object" or something like that. Brawlbox will handle mdl0 format, so you need your model to be on this format. After choosing it, you can either choose one of the objects that are part of your model or choose to combine both, which would be basically pasting the whole model in the bone you have chosen to add it.
Keep in mind your model must already be accepted by brawlbox. If you have any other formats, you will need 3ds or Maya to convert it to dae before importing to brawl format.