LTspice Monte Carlo with different model libraries
Unless I misunderstood, you can step subcircuits provided their names are numerals, so that the .STEP command can properly evaluate the variable.

For example:



R1 is defined as a subcircuit (has the X prefix, not R), and its name is parametric, {x}, allowing for a definition through the .PARAM statements. There are two subcircuit definitions, one with the name 1 (inside, a simple 0.8&Omega; resistor), and the other with the name 2 (inside a simple 0.7&Omega; resistor). The .STEP directive steps the variable x through a list with the numbers 1 and 2, corresponding to the names f the subcircuit definitions. The plot shows the values of the voltage given the stepped load.