If I move the front profiles backwards, does that reduce the space available behind the equipment?

Yes. The cabinet remains stubbornly the same depth.

Move the front profiles 30mm backwards and you gain roughly 30mm in front while losing roughly 30mm behind the equipment.

That may be exactly the right trade if a large handle needs clearance, but it can also reduce the room available for rear plugs and cable bends.

Rail adjustment redistributes the space you already have; it doesn’t manufacture any more of it.