I'm constantly changing my default paths in cache SOPs so was wondering if there is a way to change the default values?

ie I always at the very least change $HIP to $JOB and delete $HIPNAME from the path

In the long run would add up to a lot of saved time.

In the parameters panel of any node there is a gear icon next to the name field and expression language selector. Click on that and you will get a drop down menu. There is a section for saving presets and permanent defaults if you really need.
For presets, when you create a new node of the same type, you will find your defined presets at the bottom of this same menu. If you save them to your user pref dir it creates a preset folder in your houdini env folder (same as where your hda's are).

https://www.sidefx.com/docs/houdini/network/parms.html#presets [www.sidefx.com]