[bioboi]

1. There should be a black tile on your tileset, and reading from your post you already have a custom tileset so I can't really show you where it would be. But in reality your level still has the same dimensions, but you're just make it feel smaller with a black tile.

2.
if (created){
removetiledefs;
addtiledef tilesetnamehere.format,,;
}

Or if it's not using the same format as pics1.png, use a 1 in the commas, for a setup like Era's.