Can't the Board just add a rule changing the pet restrictions in the docs? How about a new rule limiting the number of units one person or entity can own? We must go to the original docs to answer that. "The authority for the board to enact a given rule or regulation must be either expressly authorized in the governing documents or Declaration of Condominium or be reasonably inferred therefrom."
If your board has adopted a new rule prohibiting pets in contradiction to the docs you are under no obligation to find a new home for Spot. The law is specific about a board's authority and the process for limiting uses and rights. Merely adding a new rule to the old rules and backdating the document does not make that rule enforceable and it might expose the directors to liability. Targeting a specific owner through such methods is doubly dangerous. Cowboy directors, if you're reading this, you are encouraged to shape up and follow the rules. If you're in an association with a renegade board, you may want to point them to this post and to this one by Jean Winters, Esq.