Rolling out an ad-density change across many pages safely

Rolling out an ad-density change across many pages safely
Don't push a new layout to 500 pages blind. My rollout:
— Pick 20 representative pages (high/mid/low traffic mix)
— Apply new density there only, tag them in your CMS
— Run 5 days, compare those 20 vs site baseline RPM
— Win? Roll to 50%, hold 3 days, watch for policy flags from scale
— Then 100%
Flagged a layout that looked great on 20 pages but tanked on long-form. Saved the whole rollout.
Steal it.