You can modify a path, or even invent new ones, such as paths with more than the pathfinder maximum of 8 legs. For example, you could make a path to determine the effect of a focusing atom on a distant scatterer. Whatever index you enter for the path will be used in the filename given to the 'feffnnnn.dat' file. For example, for the choice of index 845, the EXAFS parameters will appear in 'feff0845.dat'. A handy way to add a single scattering path of length R is to make a 2-leg path with the central atom at (0, 0, 0) and the scatterer at (R, 0, 0).
GENFMT will need the positions, unique potentials, and character tags for each atom in the path. The angles and leg lengths are printed out for your information, and you can omit them when creating your own paths by hand. The label lines in the file are required (there is code that skips them, and if they're missing, you'll get wrong results).