You'll need to check your coop's By-Laws and Proprietary Lease. Many coops - perhaps most, including ours - allow the board to modify the House Rules directly, without a shareholder vote. Similarly, deciding which contractor to hire for a major renovation is entirely within the board's authority. The board is empowered to make many types of significant decisions without the need for a shareholder vote.

Here is the text of Article XII from our own By-Laws:

"These By-Laws may be amended, enlarged or diminished either (a) at a shareholders’ meeting by vote of shareholders owning two-thirds of the amount of the outstanding shares, represented in person or by proxy, or (b) at any meeting of the Board of Directors by a majority vote, provided that the proposed amendment or the substance thereof shall have been inserted in the notice of meeting or that all of the Directors are present in person, except that the Directors may not repeal a By-Law amendment adopted by the shareholders as provided above."

Modifying the lease itself is a different matter. A material change to the lease pretty much always requires a shareholder vote. Many coops require a super-majority vote for such modifications.