How to view and customize beta of a transistor in LTspice
The other answers are OK, but there is a much easier way to do what you want, and it is not documented in the official guide.

It is the AKO "mode" (AKO stands for "A Kind Of") of the .MODEL directive.

If you define a model like this:

.MODEL MyModelName AKO: 2N2222

MyModelName will represent an NPN exactly equal to the 2N2222. For example:

.MODEL PN2222 AKO: 2N2222

You can also vary some parameters from the "base" component:

.MODEL MyBJT AKO: 2N2222 (Bf=400)

makes MyBJT a 2N2222 with a gain of 400.

Here is an hastily conceived simulation that shows what I told you:





As you can see, I just changed the value of Bf for the "AKO model" and this reflected on the output characteristics as you would expect from that change. 

This trick (AKO aliases) can be found in the undocumented LTSpice page of the LTwiki.