How can I treat a group of objects as one?

I can do what I want to do with relative ease when its one object, but when its a model of multiple it gets challenging. Is it possible to treat a model like an object with things like CFrame, etc?

Let's pretend we want to change the transparency of all parts in a model.

-- Getting the Model's Children (Only the parts with the Model as its parent)

for Index,Value in pairs(Model:GetChildren()) do
	if Value:IsA("Part") then
		Value.Transparency = .5
	end
end

-- Getting the Model's Descendants (All of the Model's parts)

for Index,Value in pairs(Model:GetDescendants()) do
	if Value:IsA("Part") then
		Value.Transparency = .5
	end
end

for i, v in pairs(workspace.House:GetDescendants()) do 
    if v.ClassName == "Part" then -- all the stuff in workspace that is a part

        v.Position = v.Position + Vector3.new(0, 0, 100)
    end -- line 1
end -- line 2

I know this is already answered with 2 answers, but I can't let you go on thinking raid6n's answer is a good idea.

So if everything in your house is inside the house model, there is an extremely simple way to move the entire model intact:

local model = workspace.House
model:SetPrimaryPartCFrame(CFrame.new(0, 500, 0))

It is that simple. The only thing you would need to do is set your model's primary part, and if you haven't already done this, I would recommend you make a small part welded to the center of the model that is invisible and cancollided false.

You can also union the parts and basically make them forcefully become one part altogether.