Techniques to add noise on top of existing terrain?

Hi, I am importing a heightmap that is rather smooth and I want to add noise on the top of it, but without changing its shape.
There is the AddNoise device I can use, but this is providing a single type of noise, not very configurable. I would like to be able to add any type of noise and idealy arbitrary heightmaps. Is this possible ?

Update: found the answer, putting it here in case it helps others: the “noise” heightmap needs to be clamped so there is no dramatic highs and lows, then I use a Ramp node to move it just above 0 (it looks almost black in mask mode). Then using a Combine node in additive mode, I just have to add the noise heightmap to the surface I want to bump.