Peregrini did not in fact include everybody without full citizenship--Latins were not peregrines, though they only held limited suffrage. Peregrines were a broad legal category, and plenty of peregrines could hold, for example, trade rights with citizens (commercium) or marriage rights (conubium). Moreover, beginning in the third century, B.C. the establishment of a peregrine praetor established more firmly the previously kind of shaky court rights of peregrines. There was also another category (actually there were two, but hostis was an archaic legal term that quickly became obsolete), dediticii, provincials whose communities had been wholly defeated by the Romans in war and who lived pretty much entirely according to ius gentium. Under the Edict of Caracalla in 212, A.D. the class of peregrines, while still technically existing, became legally obsolete, and the jurists even stop talking about dediticii.

I'm confused by what you're asking, though. Slaves could not legally be peregrines, as they were not free. Slaves were property and their legal status was as simultaneously res and persona--franchise status does not apply to them, they're not free people. Freedmen were not legally peregrines. Legal manumission resulted in the enrollment of the freedman into the citizenship, as a member of one of the four urban voting tribes (an injustice addressed several times in Republican political programs, but never successfully overturned). There were also unofficial forms of manumission, but even these resulted in the establishment of the freedman as a Latin.