I did just what Zwerkules suggested, extracting tno01_n01_04.mdl from the xp3.bif and renaming it to tno01_n01_05.mdl. Then in the tno01.set file I changed tile 248 from tno01_n01_04 to tno01_n01_05 (and put both the "new" mdl and the edited set file in a hak, of course). 5 min operation tops.
This way, you have the exact same tile twice, but you can cycle normally through all the available wall/grass tiles now and it doesn't break previous build areas.
Would be great, if you'd add this fix to PQ!
