How to modify spice transistor model
You can, rather easily, hand translate it.  The biggest headache is making sure you've got the correct variables defined.

Going off of this: http://www.youspice.com/ys/bjtfromdatasheet.3sp

And comparing it to one of the LTSpice models that is in this: LTSpice

It looks like LTSpice follows the same conventions as PSpice models, so my assumption is that the model information housed in the LTSpice link is correct for more than just LTSpice (haven't tested against NGSpice, but it's just a Berkley Spice program so it shouldn't be any different), you just need to add a new BJT with those model parameters that are outlined in the links.

EDIT: Looking even further, even AIM-Spice has the same model setup for a BJT.  I'm extremely confident that as long as you translate parameters correctly you can take any spice model and move it from one spice program to another, assuming it's at least using the basic Berkley Spice setup