Modify Attribute Definitions With the Block Attribute Manager

You can modify attributes in block definitions with the Block Attribute Manager.
For example, you can do the following:

• Modify tags, prompts, and default values. These changes do not affect the values entered when existing block references were
  inserted. For example, if you change an attribute tag from “Cost” to “Unit Cost,”
  a value entered at the prompt (such as 19.99) is unaffected.
• Reset the attribute modes. Modes control tag visibility, whether the value is a constant or a variable, the
  use of multiple-line text, the verification requirement, and position locking.
• Change the attribute text display. You can modify alignment, style, height, rotation, width (for multiple-line text),
  and whether it uses annotative scaling.
• Set properties that define the layer, color, lineweight, and linetype of the attribute.
• Change the order of display for attribute prompts. The order in which you select the attributes when you define a block determines the
  order in which you are prompted for attribute values when you insert the block reference.
  You can change the order of prompts that request attribute values.
• Identify duplicate tag names. Because duplicate tag names can lead to unpredictable results, you can set the Block
  Attribute Manager to highlight duplicate tags so that you can change them.
• Remove attributes. You can remove attributes from block definitions and from all existing block references
  in the current drawing. You cannot remove all attributes from a block; at least one
  attribute must remain. If you need to remove all attributes, redefine the block.

If constant attributes or nested attributed blocks are affected by your changes, use
REGEN to update the display of those blocks in the drawing area.

Modify Attribute Definitions With the Block Editor

You can also use the Properties palette within the Block Editor to update the definition
of a selected attribute. You can modify many of the same properties that you can change
in the Block Attribute Manager, but cannot change the order of the prompts, or how
the definition update is applied.

Apply Attribute Definition Changes to Block References

As you modify an attribute, you can specify whether the change is applied only to
new insertions, or also to all existing block references in the current drawing (the
default). If you elect not to apply changes to existing references, you update, or
synchronize, the references later using the Sync button in the block Attribute Manager
or the ATTSYNC command.