At the time when creating this wiki, there is no command in OpenRail to fill cut and fill areas on the profile.

You can create associative region by clicking in each area representing cut or fill. It can be tedious but it is associative with some limits.
If doing this is not an option on your project, you can have a look below.

Here is a way to quickly and easily create regions for that purpose:

1. Create surrounding rectangle
2. Create region, by flooding, using terrain and rectangle (above terrain for fill, below for cut)
   Select elements prior to do the flooding
3. Create region, by flooding, using proposed profile and rectangle (below profile for fill, above for cut)
   Select elements prior to do the flooding
4. Create region using intersection of regions created at step 2 and 2

youtu.be/WQFYONrpVWU