Yes. The Compaq Portable is compatible with IBM PC expansion cards, and relatively speaking it has plenty of expansion slots.
An XT-IDE or a hardcard can be plopped in with no additional hardware reconfiguration. A seperate hard drive will require removal of one of the floppy drives to make space to mount the hard drive.
The only special consideration is making sure the cards are properly secured so they don't move around.
Just FYI, the Compaq Portable and Compaq Portable Plus are 100% identical except for the case badge, and the presence of a hard disk with controller in place of a second floppy.
Supposedly some very early Compaq Portables might need a BIOS upgrade to boot from a hard drive, but I suspect those are rather uncommon (All Portables manufactured after the Portable Plus would share the same BIOS). If you do happen to come across one of those, please dump the BIOS as I don't believe it has been archived anywhere yet.