/execute as @e[type=arrow,tag=!speedy] store result score @s motion run data get entity @s Motion[0] 2000000
/execute as @e[type=arrow,tag=!speedy] store result entity @s Motion[0] double 0.000001 run scoreboard players get @s motion
/execute as @e[type=arrow,tag=!speedy] store result score @s motion run data get entity @s Motion[1] 2000000
/execute as @e[type=arrow,tag=!speedy] store result entity @s Motion[1] double 0.000001 run scoreboard players get @s motion
/execute as @e[type=arrow,tag=!speedy] store result score @s motion run data get entity @s Motion[2] 2000000
/execute as @e[type=arrow,tag=!speedy] store result entity @s Motion[2] double 0.000001 run scoreboard players get @s motion
/tag @e[type=arrow] add speedy