As far as I know there is no official way to do so.
However thanks to SetEntityMatrix - FiveM Natives @ Cfx.re Docs you can actually manipulate the scale. This does not affect the hitbox size and it can cause glitches.
E.g. scaling down a box and trying to climb on it can kill the player xD
Scaling vehicles doesn’t seem to work at all.
I am not gonna go into details on how to use that function to scale entities as doing it properly via the matrix provides a whole lot of math problems.
Code and Video of my initial tests
RegisterCommand("scale", function(src, args, raw)
local entity = PlayerPedId()
local _, _, upTemp = GetEntityMatrix(entity)
Citizen.CreateThread(function()
while (true) do
Wait(0)
local forward, right, up, position = GetEntityMatrix(entity)
SetEntityMatrix(entity, forward, right, upTemp + vector3(0, 0, -0.8), position)
end
end)
end, false)