Can the park manager force rules on some residents and not on others?

No. The MRL provides that the park rules and regulations have to be “reasonable.” (Civil Code §798.56(d)) “Reasonable” often may be subject to court interpretation, but normally rules have to have some rational basis in

fact under the circumstances, as well as apply evenly to everyone residing in the park. Park owners and their employees are required to abide by park rules to the same extent as residents have to, except rules regarding age
limits or acts of the park owner or park employee undertaken to fulfill park maintenance, management or operational responsibilities (making noise by pounding nails, use of trucks for maintenance purposes, etc.). (Civil
Code Sec. 798.23)

Recap:
● Park rules shall be applied evenly to everyone residing in the park.