Can i set up my premiere project so that it is referencing titles in .prtl files rather than imported titles becoming part of the current project file? I would like to be able to edit them outside of my current project.
When you import files into PrP, it basically creates a pointer to that file wherever it is located, unlike FCP which in many cases actually transcodes the file.
For example, if you have a Photoshop file in PrP, you can still open that files and alter it in PS.
Short answer: you cannot edit a Premiere title outside Premiere.
However you can edit them in any project you want.
I would like to be able to edit them outside of my current project.
To do that, you will need to use something other than the native .prtl format. Probably the most common recommendation around here is to use Photoshop for the job.