Simple answer is yes but the screw in "plug" section normally has a soft face to provide the shut off. Newer models have a "dowty" type seal under the cover cap but older ones used a fibre washer that overenthusiastic tightening could split. Also you should really plug the hole left when the pipe to the fire is disconnected. A 1/4"bsp screw in plug with thread seal is one method. If the olive on the gas fire connection pipe is a soft version be careful not to damage it on reassembly. Finally check gas tightness with a leak test fluid unless you can carry out a full soundness test.