We have therefor provided our Tilebrush to UO mappers who would like to use default tiles and have the transitions "paintable."
Replace your current TilesBrush.xml and TilesGroup.xml in your LocalData folder with these files. To access the Tilebrush in CentrED+, select Allbrushes in your item menu and select the brush you want to "paint" with.
This tilebrush will work with a default UO install. Make sure to back up your existing files if necessary.
Have fun, and happy mapping!