Place command block where other command block was before and change its content.
Press ctrl+mouse wheel to copy its nbt.
Observed result
A copy of the command block that was initially in place is in the main hand.
relates to
MC-270413A nbt copy of a block is ABSOLUTELY the same as the first nbt copy of the original and n (+nbt) display for tooltip of (a copy of)×n a block have an "Items" block data
Resolved
MC-270462Pick block does not work on structure blocks that are filled out with info