Related Clues:

• Correct (one's ways)
• Accessory device
• Supplementary item
• Feature supplementing standard model
• Alter in detail
• Modify formally
• Enlarge the house
• Accompaniment
• Architect's afterthought
• Alter a text
• Fix the Constitution
• Like some fees
• Build a new wing, say
• Update, perhaps
• After-market item