In a word… no. Many people believe partially or fully closing off a floor or ceiling supply vent will help redistribute air flow to other areas of a home. Unfortunately, with the way duct systems work, this typically causes unwanted whistling and static pressure buildup.
Air circulation in a home works by the difference in pressure. Once a fan blower starts, the supply ductwork becomes a positive pressure zone and the return ductwork a negative pressure zone. Air likes to move from positive to negative pressure. Closing off the endpoint of a duct run causes a pressure buildup at the point of entry for air. This air cannot reverse flow against the static pressure and will eventually leak out into the crawl, attic or cause noise as it forces its way across the closed off grille vanes.
The best solution is to close off supply ducts where they connect to your furnace or air handler, increasing the likelihood this air will be properly redistributed elsewhere in your home.
Craig Sopo 