You can modify a block definition or a block reference already inserted in the drawing.
When you redefine block definitions in your current drawing, both previous and future insertions of the block in the drawing are affected.
You can change the color and linetype of the objects within a block only if the objects in that block were created with floating properties.
You can edit the values of attributes that are attached to a block and inserted in a drawing.
You can edit the values and other properties of all attributes that are already attached to a block and inserted in a drawing.