Many variables like $HFS expand to shortened paths like C:/PROGRA~1/SIDEEF~1/HOUDIN~1.590

I encountered a situation in PDG Deadline where this variable is passed to Deadline in this ~shortened form, and causes errors because of it.

How can I convert this to the actual path?

I'm not sure if it would work, but possibly expand it through a python expression? Something like hou.expandString('$HFS') docs [www.sidefx.com].
You could also just put the whole file path in there if you have multiple variables and it will then return the whole path string for you.

Unfortunately, that just returns the shortened ~ path.