@User, when done placing the symbol, descend into the symbol ('i' key), then without clicking objects press 'q' to edit the symbol global attributes, change the 'type=subcircuit' to some 'type=mysymbol' ; mysymbol can be anything as long as it is not 'primitive' or 'subcircuit' . This way xshem will not try to look for a corresponding schematic. see the relevant manual page for details. The symbol will be unbound so you have to include the spice netlist for it. Ensure the port order is identical between symbol and spice netlist implementation.