Rolling pre tubes question

Jazzman, I always follow the manufacturer's suggestion. I just try to find the lowest noise version of the type. RAM Labs tests their tubes for noise and put the speck right on the box.
Any labels on the tube should be removed. I always turn the unit off before I remove tubes even if they are not that hot. You do not want any impulses getting to other equipment. If the unit is disconnected it is off anyway. 
If you really want advise from the hourse's mouth call Manley and ask.

I can’t add anything, far as advice, to what mijostyn posted, but- that Brent Jesse Recording, Upscale Audio (Kevin Deal) and Vintage Tubes Services (Andy Bouwman) are all excellent sources, for noise-tested/rated tubes and accurate information.                  Of course; Kevin Deal is also very familiar with your Manley, being a dealer.

NOT TO YELL - BUT RESPONSES IN CAPS BELOW

1. Should amp be turned all the way off, or is stand by OK when changing tubes ?  OFF ALL THE WAY ALL THE TIME
2. Tubes that have paper labels glued on them ( Brimar CV 4033 ) OK ?  BEST REMOVED, ESP FOR POWER TUBES
3. Can input tubes ( 12 at7's or the Brimar CV 4033's ) be substituted for the driver tubes...6414 ? I have read that      6414 can be substituted for 12 at7's but what about visa verse ?  SEARCH ONLINE FOR TUBE INTERCHANGEABILITY... GETS TRICKY SOMETIMES, DEPENDS NOT JUST ON THE TUBES BUT THE CIRCUIT THEY ARE WORKING IN... CHECK WITH MANUFACTURER BEST IDEA
 I have use the Brimar CV 4033 in the 12 at7 input spot and enjoy the sound, so was wondering about it as a driver ?  INPUT TUBE MORE SENSITIVE THAN DRIVER/BUFFER IN CHANGING SQ
4. What tube is more impact on the sound , input or driver ? SEE 3
5. Ideas for rolling the 6414 as i do not see many around ?  https://audiokarma.org/forums/index.php?threads/0528-6414-12au7-equivalent.493894/

If you have a preamp where you need to remove the cover to access the tubes you need it to be off (and best unplugged) for about 30 minutes first before rolling tubes to insure hazardous voltages in the power supply have had time to discharge. Not matter what you should NEVER change a tube w/o powering down first.