I would like to rotate an object based on a point attribute from te point it's copied to. So I can paint the rotation of copied objects.

For instance, to keep it simple, I've created a grid ,created an attribute called ‘rotateValue’, a paint sop wich modificates the ‘rotateValue’, I've copied a box to every point of a grid.

But so far it doesn't work, any suggestions?

try copy/stamp for rotation and painting $PSCALE for scale.

also if you don't mind painting with curves you can
massage curve normals and just blend them with
the canvas normals fake rotation.
attached scene is animated.