How to (.step) change bjt/fet/opamp models in simulations in LTSpice?
You can do this by using a little trick: the .param statement in Spice only works with numbers, but Spice has a way to rename models with numerical names, the ako (Also Known As) option. IIRC, this may not be documented in LTSpice docs, but it does exactly what you want. See ltwiki:AKO Aliases (A Kind Of) for a little more information 

To sweep models, simply use .model n ako:&lt;name&gt; to rename each model you want to sweep, and then use a .step param MParam list 1 2 .. n to sweep through those models. See below for an example, where I sweep through three simple diode models plus a "real" diode model.