Thanks for the question! I think some of it is new here. Let me point to the one place in the canon you may have missed. The second paragraph of canon 603 reads: [[ §2. A hermit is recognized by law as one dedicated to God in consecrated life if he or she publicly professes in the hands of the diocesan bishop the three evangelical counsels, confirmed by vow or other sacred bond, and observes a proper "program of living" (Rule of Life) under his direction.]]
Note the word "proper" above. It is not a "Britishism" like, [[Though he was from the US, John still knew how to brew a proper cuppa (tea)!!]] In the Church, we have Canon, or universal law, and Proper, or particular, law. A canonical (established and normative) religious congregation, for example, is bound by canon law; all such institutes are thus bound. At the same time, each institute has a separate document or documents representing its own proper law (constitutions, and statutes) which allows members to govern themselves according to their own unique qualities, mission, and charism. While an institute's constitutions are ultimately canonically approved by Rome or their diocese, for instance, they are specific to the institute and composed by the professed members. After all, they are the ones who have been called by God to embrace and live the universal elements in ways members of other congregations have not been.
Thus, in an analogous way, the hermit's Rule of Life represents her own "proper law"; it complements and specifies (applies in specific and proper ways) canon law in a solitary eremitical life. The canonical elements every hermit lives are listed prior to the term "program of life" These include the elements of paragraph #1 (stricter separation from the world, assiduous prayer and penance, the silence of solitude, a life lived for the salvation of the world, etc.), and commitment to the evangelical counsels, a Rule of Life lived under the bishop's supervision in paragraph #2. The "program of life" or "Rule" specifies the ways in which this hermit lives these elements in order to respond to God's uniquely personal and ecclesial call, and honors both the unity and the diversity of that vocation. Thus, canon 603 itself calls for a combination of universal and proper law allowing the hermit to tailor the terms of the canon in order to achieve the flexibility necessary to serve faithfulness to the vocation. This tailoring will not represent a mitigation of the terms of the canon, but rather, an exploration of their depths over time.Bearing this in mind, we have the answer to both of your questions. First, the c 603 hermit writes her own Rule, she does not merely adopt a Rule written by someone else, because the Rule grows out of the values and praxis of eremitical life generally, but also out of her own relationship with God through her life and especially her life in the silence of solitude. The Rule must do justice to both of these dimensions! And second, a bishop supplying a ready-made Rule for hermits in his diocese actually has failed to take not only the terms of Canon 603 seriously enough, but the very vocation it codifies as well. (I wonder that a non-hermit bishop would even believe he could do such a thing.) By the way, this observation would also apply to a so-called Laura of hermits whose members fail to write their own Rules. Canon 603 is written for solitary hermits and requires that each one of us write our own.
All of this is the foundation for my comment in other articles that I thought the authors of Canon 603 had written well, perhaps better than they knew (though now I think they really knew exactly what they were doing!). All of this is also at the heart of why I find Canon 603 to be truly beautiful in the way it combines the constraints of law and the freedom of eremitical life. Finally, this combination of universal and proper law allows for an approach to the discernment and formation of such a vocation that relies on the gradual composition of a livable Rule rooted in the individual's lived experience and undertaken in collaboration with diocesan personnel and, if possible, the accompaniment of an experienced diocesan hermit. It takes time to "penetrate" the terms of the Canon and come to understand and live them deeply enough to see they are doors to the Mystery which is God and the hermit's relationship with God, not terms with a single fixed and infinitely more superficial meaning. Writing one's Rule is part of this process of "penetration" and a way one learns to be ever attentive to ongoing formation as well.