I want to change the EQ on a track on just a very small 2 or 3 second section. How can do this in a non-permanent way if I want to change it back? Is there some way to do an envelope with nodes to effect an EQ change?

Yes you can, if your EQ is automatable. If you have the Sonitus EQ, that is automatable.
Insert it in the FX bin, click the W button in the track pane, click play, and move the sliders. Those movements will be written into the track as an EQ envelope and will play back as you set it.

Also, once that envelope is created, you can manually fine tune it, if needed.

Does HS support Clip Fx?

If so, you can split the section you want the EQ applied to into it's own clip and put a clip EQ Fx on there.