Thanks for reporting your experience, every bit of information we learn helps as we sail these uncharted waters.
I think it’s possible that the issue wasn’t personal use v. commercial use per se, but that you ran afoul of the first come first served rule pursuant to this clause in the governing documents “no owner may directly rent,…without making a prior reservation…on a first come first served basis. DVD’s approval of a rental by an owner is not required after a reservation has been made in the renter’s own name.” Maybe CMs have been instructed to not allow lead guest name changes if the reason for doing so is because the owner is renting the reservation & to instruct the owner to cancel & rebook in the renter’s name pursuant to this clause & the CM wasn’t happy about having to deal w/ enforcing the new guidance.
If it were me I wouldn’t complain too loudly & risk having my reservation scrutinized & possibly cancelled, but I’m very risk averse

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OTH, sometimes CMs misunderstand, or meaning is lost in translation, or they’re confused. This is new to them just like it’s new to us.
My most recent telephone call w/ a DVC CM took forever to buy 5 date based tickets & 2 Sorcerer’s passes & the CM’s understanding of eligibility to buy sorcerers passes was incorrect, but after an hour+ I managed to make my purchase.