CAD tip # 13578:

The values of constant attributes are stored in block definitions (and so they are identical in all instances), the values of variable attributes are stored in block references (and so they may differ in each instance).

Download the LISP utility from Download, load it into your AutoCAD with APPLOAD and then type the command ATT2CONS to convert to constant attributes or ATT2VAR to convert to variable attributes. You can specify the attribute by picking in the drawing (picking an example). All these attributes in all references of that block will be modified. The drawing will usually not change visually. When converting variable attributes to constant ones, the default value will be used (and the original variable one will be lost).