IANAL, but I did stay at a Holiday Inn Express.
MCL 28.422 License to purchase, carry, possess, or transport pistol; issuance; qualifications;
applications; sale of pistol; exemptions; nonresidents; basic pistol safety brochure;
forging application; implementation during business hours.
Sec. 2. (1) Except as otherwise provided in this section, a person shall not purchase, carry, possess, or
transport a pistol in this state without first having obtained a license for the pistol as prescribed in this section.
(12) This section does not apply to a person who possesses a pistol if all of the following conditions apply:
(a) The person is not otherwise prohibited from possessing a pistol.
(b) The person is at a recognized target range or shooting facility.
(c) The person possesses the pistol for the purpose of target practice or instruction in the safe use of a
pistol.
(d) The owner of the pistol is physically present and supervising the use of the pistol.
MCL 28.432 Inapplicability of MCL 28.422; amendatory act as “Janet Kukuk act”.
Sec. 12. (1) Section 2 does not apply to any of the following:
.....
(f) A United States citizen holding a license to carry a pistol concealed upon his or her person issued by
another state
.....
(i) An individual carrying, possessing, using, or transporting a pistol belonging to another individual, if the
other individual's possession of the pistol is authorized by law and the individual carrying, possessing, using,
or transporting the pistol has obtained a license under section 5b to carry a concealed pistol or is exempt from
licensure as provided in section 12a.
If the pistol isn't registered to you, you can carry it only at a range and only if the owner is present. If you have a Michigan CPL, you can carry a pistol registered to another individual as long as you are in lawful possession. (i.e. have permission). Grey area is whether a non-Michigan CPL allows for carry of another's pistol, registered in Michigan or otherwise.
I've instructed my wife that if I ever need to go to a hospital (CPFZ) while carrying, she is to have a LEO disarm me and take possession. She also cannot be in the car with my pistol(s) properly stowed in the trunk for transport, unless I am present and in "possession". (no quick run into a store and leave the wife in the car) I know another couple where the spouse applied for a CPL for these reasons.