Hey, I followed exactly what you did and a few things bugged up.
1) I could only edit the very first OW in the new table, then every time I tried to go to an Index above 0 I would get "Error 36 (Bad record number) in procedure Load Sprite Structure of frmOverworldEditor" and the Width and Height for the Index's above 0 are all -1. Not exactly sure what I did wrong. I did change the palette from the original one when I loaded my first OW, like I replaced the Palette that is used for the Hero with my own Palette with the option when you import a image. Does that matter? I literally copied everything you did with a new rom, so it's not like I already used up the space or anything.
2) When I try to click any Map in Advanced Map it freezes and closes. I never had this problem prior to trying to do this.
I did keep a back up and try this again tomorrow, but help would be appreciated :p