Dear Dr. Bowring,
Thank you very much for your response.
It seems to me that this interpretation is somewhat unlikely. Since the document is in a private collection, I haven't been authorized to disclose it verbatim, but the general structure is as follows. First, three clauses are introduced, where the recipient is encouraged to practice benevolence and righteousness, strive for further perfection, and exhibit exemplary moral character. Then the final clause says "
多年御出精ニ付此度令免印者也." It is also known that the recipient had received a 免許皆伝 from his master (who also happens to be the issuer of the document) some years prior to that, so the next logical step would have been to grant him with an official 印可状.
In a private communication, Dr. Yoshihiro Man'i has suggested that the compound 免印 may be a kind of shorthand for 印可を免(ゆる)す, which is certainly 和習, but makes quite a bit of sense nonetheless. Alternatively, the compound may be a contraction of 免許印信 or some similar locution.
Having weighed the pros and cons of the two interpretations that have surfaced so far, I tend to favor the 免印=印可 one, but if someone here has encountered the compound 免印 in their research, I'd greatly appreciate their input.
Best regards,
Mikhail