Use modifier on group?

I will try to explaing as good as possible what i mean.

Lets say i an cloud displacement modifier on one object to add some noice. and then i makes alot of copies of this object. e.x. into a wall

Can i then add all these into a group and add an “global” modifier to make a “lower res”(adding a more random look to the object/wall as whole) noice displacement that addes noice as if it all was one object?

merging them all into one object is one option i know, but then i loose al my modifyers

You can’t have one interactive modifier that applies to a whole group in Blender, but there is a way to get what you want. Put the modifier on one of the objects and set up the parameters as you see fit. Then select all the objects you want the modifier on. Select the one object with the modifier on last to make it the active object (selected and active are different things in blender, it took me a while to figure that out when I first started out.). Select Object->Make Links->Modifiers from the bottom menu. The active object’s entire modifier stack will be copied to all the objects. You’ll have to do this every time you want to change the modifier’s parameters, so you can add all the objects to a group to make that easier, but it isn’t strictly necessary. Be warned that if the objects you’re copying to have any modifiers of their own, this will obliterate them.