Can a registered patent practitioner file papers without being of record?

Yes, registered patent practitioners can file papers in patent applications and reexamination proceedings without being of record. MPEP 405 states:

Papers may be filed in patent applications and reexamination proceedings by registered attorneys or agents not of record under 37 CFR 1.34. Filing of such papers is considered to be a representation that the attorney or agent is authorized to act in a representative capacity on behalf of applicant.

This means that by filing papers, the practitioner is implicitly stating they have authorization to act on behalf of the applicant, even if they are not officially recorded as the attorney or agent of record.