I want to move my TV location 10 feet over. Is it O.K. to extend the RG6 with a coupler to the new location and blank off the coupler location with a blank plate so it is still accessible? Will this effect signal quality?

Yes, it will affect the signal strength, but you'll never notice it. Rock on.

So long as you do use a proper coupling, of course, and not the "twist and tape" style of extension.