If the declaration expressly permits, a unit may be subdivided into two or more units. A unit owner shall prepare an amendment to the declaration, including the plat, which identifies the unit involved, specifies the boundaries of each unit created and its dimensions, assigns an identifying number to each unit created and allocates the allocated interests formerly allocated to the subdivided unit to the new units in a reasonable manner. The amendment shall be executed by the owner of the unit to be subdivided and, before recording, submitted to the board of directors. Unless the board of directors determines within thirty days that the proposed amendment is unreasonable, which determination shall be in writing and specifically state the reasons for disapproval, the association shall execute its approval and record the amendment.