Hello @Howan,
Thanks for reaching out to us.
You can simply assign a first material using only the displacement texture you want to use, then assign a second material to the plane object with the desired textures for Bump and/or Normal channels (a rocky material, or a sand material, etc.)
In this case, the displacement considered will be the one from the first material.
In case you want to use multiple displacement textures, you can use a Layered material instead.
I'm attaching a sample scene (I over-exaggerated the values just to notice the effect) so you can explore and experiment with the scene file.
I hope this helps.