on our Raypaul and Anatol Mariah dryers i have turned off the gas while the dryer was on so that it uses all the gas in the pipe - ensures that the correct gas valve was turned off. use a valve lock and tag to ensure the valve cant be accidentally turned on while working on the dryer.
i have removed, cleaned, and reassembled the burners on our Mariah dryer, and the procedure above seemed to work okay for us.
five years ago i had the Maxitrol M611 modulating gas valve changed on our Raypaul. i ordered the part and my friend that works on gas and oil came in and swapped the valves. nothing unexpected happened. he took the gas train out, removed the old valve and put the new one in.