Oh! I didn't realize I was in the wrong print properties area. So two useful things to note.
1) The printer is still definitely sending jobs to the old port, rather than the new one I created.
2) When I go to the actual printer properties page it seems to be giving me the choice to switch to the new port. Sadly it's all greyed out and I can't actually click any of the boxes, which I assume is its way of telling me I have to be in admin mode to do it? Which if that's it then maybe hopefully problem solved when I eventually get that username and password.
Looks like it is a shared driver,so you would need to be on the Print Server itself to make the change.
In either case, you do need admin privileges