Summon a falling block using the summon command:

/summon minecraft:falling_block ~ ~ ~ {NoGravity:1,Time:1,BlockState:{Name:"minecraft:stone"}}

(Note, falling block may disappear after a while, so it may be necessary to constantly merge Time:1 with its NBT)

Use a data merge command to modify the falling block's blockstate:

/data merge entity @e[type=falling_block,sort=nearest,limit=1] {BlockState:{Name:"minecraft:red_concrete"}}

Note that the falling block does not change to the inputted blockstate.
Check the NBT of the falling block using:

/data get entity @e[type=falling_block,sort=nearest,limit=1]

Note that the returned data clearly says the falling block's blockstate name matches the inputted data from the data merge command.
The falling block, upon its blockstate being updated, should also update its appearance to match its new NBT data.