Here's my simple, logical passive-voice version of the sentence where the subject in the original sentence (carrier) becomes part of the predicate and the object (manufacturer) of the verb (requires) becomes the subject.
"The manufacturer is required by the carrier to install the software code on the iPhone."
As for your question, "Did I change the meaning of the original sentence in the passive sentence?" I would say, No, because the essence is still there. But most conversions from active to passive voice usually merely makes the subject part the predicate, and the object of the verb as the subject. That being the case the focus is now on the subject "manufacturer."
In the other versions offered, the verb tense used has been changed:
Elian used "shall be" which is not consistent with the present tense of the original sentence.
MrsLannister used "can." MrsLannister constructed the passive voice to mean that "software code can only be installed by the iPhone manufacturer" which is nowhere to be found in your original sentence.
In the version of user82023, "carrier" is still the subject, so there seems to be no real change from active to passive. Moreover, the essence (that the manufacturer is the one directly required by the carrier to install the software...) was lost.