What needs to be modified with 4" or smaller lift?

With a 4" and smaller suspension lift, you do not need to lenghten your driveshafts. Some extreme offroaders may find that they will need to lenghten their driveshafts a little with a 4" lift due to extreme articulation and catching air, but typically you do not need to do this.

Also with a 4" or smaller suspension lift, you will not need to lengthen your brake lines. What you may have to do is loosen the brake line clamp that holds the brake line to the frame, that way it could slide down due to the lift. Then reclamp or retighten it when you are done lifting.

There may be other things you will have to loosen in order move things around, like the 4 wheel drive indicator light wires that go to your cad unit on cad equiped axles.

Just keep an eye out and frequently check to make sure nothing is getting pulled or is too tight when lifting your vehicle.