HONG KONG, Nov 11 (Reuters) – A senior Hong Kong cultural official mentioned on Thursday that flexibility of expression was not higher than a China-imposed national protection regulation, on the eve of the opening of a present-day artwork museum supposed to put the city on the international cultural map. The multi-billion dollar M+, showcasing contemporary artwork from top Chinese, Asian and Western artists is Hong Kong’s bid to match museums like the Tate Fashionable in London, the MoMA in New York and the Centre Pompidou in Paris. But the imposition of a sweeping national security law by China final 12 months on its once freest metropolis is casting a pall…