This command can be found under Draw Field to Finish → Edit Codes → Code Table Settings → Substitution Codes and is used to convert raw field codes to be able to be processed through Field-to-Finish.
If for example your field staff have codes that they use but the client (e.g. Local Council) requires others, than this command can be done post-processing of the Field-to-Finish to get the required results. The command can also be used if the field staff used the wrong codes.
Use the Import and Export functions to load and save substitution codes to a comma separated text file which are stored in a file named f2f_sub.dta in the %appdata%Carlson...USER folder.