I usually do it this way.
I open the file set and control the us of the tiles looking for a same configuration, it is very important that the sides and the streets of siao tiles of the same type of ground, otherwise the tiles will not be displayed if they are not necessary to do it again by hand. Rename with a free serial number next to the type of tile you want to use to have a certain order.
I create a copy of ugule tile and published the name and map name, save the changes.
If the tile has to be part of details or groups, you have to insert it into a new group from the third drop down.
Once everything and done, save the file set and itp files.
The program saves both, there are two entries saved in the bottom.