Here is a simple way to make a variable resistor in LTspice.
Right click the resistor you want to be variable and give the value a curly bracket name.
Here I used R for simplicity. So the value of R2 was entered as {R}.
Click on .op (far right, top corner) and enter a step parameter for R.
Here the value for R2 was set to step from 1ohm to 1000ohms in steps of 100.
.step param R 1 1000 100
Result above in a very simple circuit.
Hope this helps someone.
