This may be a stupid question, but I can't quite figure it out. For an academic career, it seems to be quite important to be "principal investigator (PI)" on cool research projects. Now, say for some reason you're not eligible to be an official applicant on a grant proposal (e.g., because you're abroad and the funding agency doesn't permit that), but you're still involved as a project leader, providing important scientific stimuli, attending meetings, etc. - can you still call yourself a "PI" (as long as all involved parties agree), or is that an official stamp that really only the formal appointee of the grant receives?
To make it a bit less hypothetical: I'm thinking about writing a grant proposal with my former supervisor for funding a PhD student at his institution, with me co-leading the supervision of the student. I'm currently abroad, doing a PostDoc at another institution, and I'm trying to figure out whether there's a way I can be involved in that project and receive "official academic credit points" for it. ;-)