This might help, Convert UK national brood frame to langstroth in 1 minute - #14 by Coco
Great to have your questions.
- you could alway step by step cut out comb and put it in the langstroth frames, dont do it all at once as it is too high a risk. (The longer comb is in the sun the easier it starts to break apart and honey attracts other bees and then you might end up with the bees being overworked in rebuilding that they get robbed.)
2)The method of checkerboarding might be good, often used to cycle out old frames. I wouldn’t do it all at once again, But add the Langstroth brood box then swap out say 2 brood frames from the bottom box and move them up to the top with empty frames put in there place in the bottom box. Alternate the frames so there is an empty one between two worked frames. It depends on the strength of the colony, you dont want to do this with a colony that doesnt have the bee population to support 2 brood boxes. Then once the two old frame moved up to the top have hatched and the bees have used the resources to build new comb in the empty frames below, remove them entirely.
- Id probably forgo this unless you are actively splitting to prevent a swarm, and go with the option 2 when the colony is stronger.
It is a hard one to predict as you need to have the colony to know for sure what will work for them. You may find that you are able to cycle out old frames naturally as part of the colony establishing the single brood box too. As the bees build out new frames, assess whether any old frames came be removed, Usually edge frames will have honey stores predominantly, so these can be the first to go, then the bees make another of the edge frames for honey stores and repeat removing old frames over time until the bees are all in new frames. If you dont want to take their resources, you might consider feeding the honey back to the bees, crushing the removed comb straining what you can and then using a DIY feeder.