How to Pulse AND Step a Load in LTSPICE
I recently had some pretty extensive requirements along these lines and ended up discovering four fundamental methods. For your application I think method 3 is going to be the winner, but let me outline them so you can evaluate:

Method 1: .step

As in your question, simple but no time domain control.

Method 2: Switch Model

As in winny's answer. The presence of the switch model in the current path complicates things.

Method 3: Variable Parameters

Set your resistor's resistance to an expression involving V(netname), and then drive that net with a variable voltage of your choice.



Very simple to include in circuit and very powerful to control because you can use any voltage source circuit. For example, in your case you can drive setpoint with a pulse voltage source and a PWL voltage source to get step and pulse behaviours.

Method 4: Behavioural Sources

Similar to Method 3, but use a behavioural source (bi or bv) instead of a passive component.



Adds the extra feature of controlling a source rather than a sink.