How can I disable bodyparts/packs?

I found this solution through google:

Make the default rig a blank desired rig, for example a blank R15 block rig, set the character to it and then load character appearance into said rig.

https://devforum.roblox.com/t/remove-certain-packages-bundles/195129/4

So to do this, you have to first create a blank R15 block rig using the default Rig Builder plugin. At the top of your Roblox Studio, there is a "Plugins" tab. Click on it and find "Rig Builder". When you click on Rig Builder a GUI should pop up asking what type of rig you want. Choose "R15 Block Rig". It should create a block rig in front of you.

Then you have to move that rig from workspace to game.StarterPlayer.StarterPlayerCharacter, and rename it to StarterCharacter.

Then you have to use Humanoid:ApplyDescription to apply the humanoid description of a player to their own character whenever they respawn.

Add a normal Script to ServerScriptService and paste this code in:

local Players = game.Players

Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:Connect(function(character)
        local humanoid = character:WaitForChild("Humanoid")

        local humanoidDescription = Players:GetHumanoidDescriptionFromUserId(player.UserId)
        humanoid:ApplyDescription(humanoidDescription)
    end
end)

How the code works is, whenever a player joins (PlayerAdded), the script listens to when the player's character respawns (CharacterAdded) and gets their humanoid description and applies it to their humanoid.