Related Clues:

• Attach a codicil to
• Change (a will)
• Modify, as a motion
• Add to, as a bill
• Improve a text
• Garage, perhaps
• Building wing, e.g.
• Extra, and this puzzle's title
• Reform
• Alter, as an agreement
• Include as a bonus
• Congressionally change
• Limelight sharer
• Change formally
• Build an annex