Courageous cannot be enlarged into a 35,000-ton carrier

Could the Courageous-class conversions use the treaty's 35,000-ton allowance to become much larger carriers?

No; the original hulls were about 19,000 tons standard and gained roughly 5,000 tons in conversion, so adding another 10,000-15,000 tons would overstress the structure and amount to building a new ship.

Removing guns and rearranging armor provides only limited weight for a flight deck, island, hangar, and aviation systems. Admiral- or G3-class hulls could plausibly approach the 35,000-ton carrier category, but Courageous and Glorious lack the framing and volume for that scale of growth.