Is it Possible to make a GAMEPASS from a KEYDOWN function?

Yes, of course, but you'll need a RemoteFunction to return whether you own the game pass from a LocalScript. The jump Bindable should also be disabled. You can also view this for some extra knowledge.

LocalScript in StarterCharacterScripts

local me = game.Players.LocalPlayer
local char = me.Character or me.CharacterAdded:Wait()
local humanoid = char:WaitForChild("Humanoid")
local RemoteFunction = script:WaitForChild('RemoteFunction')
local UserInputService = game:GetService('UserInputService')
local canJumpAndRun = RemoteFunction:InvokeServer()
-- Invokes the remote function that return whether you own the game pass
	-- only checks when they load though, so if they buy it after, they'll need to reset. 
	
local ContextActionService = game:GetService('ContextActionService')
ContextActionService:UnbindAction("jumpAction")


local maximizedWalkSpeed = 30
local defaultWalkSpeed = 16

UserInputService.InputBegan:Connect(function(input)
	-- Something was pressed
	if input.KeyCode == Enum.KeyCode.Space then 
		-- Will need a loop to check if we're holding to keep jumping
		humanoid.Jump = (canJumpAndRun and true or false)
	elseif input.KeyCode == Enum.KeyCode.LeftShift then 
		humanoid.WalkSpeed = (canJumpAndRun and maximizedWalkSpeed or defaultWalkSpeed)
	end
end)

UserInputService.InputEnded:Connect(function(input)
	-- Key up
	if input.KeyCode == Enum.KeyCode.LeftShift then 
		humanoid.WalkSpeed = defaultWalkSpeed
	end
end)

In a Script inside of the LocalScript

local RemoteFunction = Instance.new("RemoteFunction", script.Parent)
local GamePassService = game:GetService('GamePassService')
local GamePassId = 100000

function RemoteFunction.OnServerInvoke(player)
	return GamePassService:PlayerHasPass(player, GamePassId)
end