I'm also going to point out that changing tiles (in my case I needed solid tiles on one Tilemap and floor tiles on another) is as simple (yet tedious) as opening the XML in Notepad++, copying the tile data string (the long line of numbers and commas), then paste them into a new file. Replace solid numbers with "-1". IE: if your wall tile is "45", in Notepad++ open "find and replace, and look for ,45, and replace with ,-1, (include the commas in case the tile numbers are super high, this way lower numbers will not change when you don't want them to).
Do the same with floor tiles in the OTHER string.
When done, copy the string back to the main XML file, save, and load your project file.