Stripped down

local moddedCos = {		-- keeps track which trinket is in the player posession
	YourTrinket = false			-- ex. BloodyCobweb = false
}

-- trinkets
TrinketType.TRINKET_YOUR_TRINKET = Isaac.GetTrinketIdByName("Your Trinket")
-- costumes
Mod.COSTUME_OF_YOUR_TRINKET = Isaac.GetCostumeIdByPath("gfx/characters/yourtrinketscostume.anm2")

function Mod:setTrinketCostume(consol,para)
	if consol == "onPickup" then
		if moddedCos.YourTrinket == true  then
			ctc:SwitchCostumeRequirement(TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET)
			if switchTrinketBoolean == true then
				moddedCos.YourTrinket = false
				switchTrinketBoolean = false
			end
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_EXECUTE_CMD, Mod.setTrinketCostume)

function Mod:onNewRun(bool)
	if bool == false
	and trinketCostumesMod then
		moddedCos.YourTrinket = false
	end
end
Mod:AddCallback(ModCallbacks.MC_POST_GAME_STARTED, Mod.onNewRun)

function Mod:onModdedCostumeUpdate(_)

	if trinketCostumesMod then
		for i = 0, (game:GetNumPlayers() - 1) do
			local player = Isaac.GetPlayer(i)

			if player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET)	 -- still have to check if the player has the trinket
			and moddedCos.YourTrinket == false then
				ctc:AddTrinketCostume(player, TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET)
				if switchTrinketBoolean == true then
					moddedCos.YourTrinket = true
					switchTrinketBoolean = false
				end
			end
			if (not player:HasTrinket(TrinketType.TRINKET_YOUR_TRINKET))
			and moddedCos.YourTrinket == true then
				ctc:RemoveTrinketCostume(player, TrinketType.TRINKET_YOUR_TRINKET, Mod.COSTUME_OF_YOUR_TRINKET)
				moddedCos.YourTrinket = false
			end
		end
	end
end
Mod:AddCallback(ModCallbacks.MC_POST_UPDATE, Mod.onModdedCostumeUpdate)