From the forum 10/2/2017:

It’s quite easy to add a new setting. For F2/m then first find the primitive version in SGCOM5.CPP which is P2/m (space group number 10). P2/m has a file in the sg directory called P2OM.SG and part that file looks like:

xyzs
{
                x, y, z 
                -x, y, -z 
                x, -y, z 
                -x, -y, -z 
} 4

The computer adapted symbol for P2/m in sgcom5.cpp looks like: 10 MCI1A000P2B000 { p2/m = p12/m1 = 10 - p112/m - p2/m11 }

To add a line for F2/m then simply use: 230 MCI1A000P2B000 { F2/m }

This will produce a file called F2OM.SG and part of it looks like:

xyzs
{
                x, y, z 
                -x, y, -z 
                x, -y, z 
                -x, -y, -z 
                ' +(1/2, 1/2, 0) -------------------------
                x+1/2, y+1/2, z 
                -x+1/2, y+1/2, -z 
                x+1/2, -y+1/2, z 
                -x+1/2, -y+1/2, -z 
                ' +(1/2, 0, 1/2) -------------------------
                x+1/2, y, z+1/2 
                -x+1/2, y, -z+1/2 
                x+1/2, -y, z+1/2 
                -x+1/2, -y, -z+1/2 
                ' +(0, 1/2, 1/2) -------------------------
                x, y+1/2, z+1/2 
                -x, y+1/2, -z+1/2 
                x, -y+1/2, z+1/2 
                -x, -y+1/2, -z+1/2 
} 16 

Note, I don’t know what space group number to put for F2/m so I put 230 and I put the line at the bottom of the file. It’s up to the user to ensure the correct crystal system (ie. correct lattice parameter constraints).