If you print too many hardbacks, do not despair. You can publish a paperback by stripping and rebinding your surplus inventory and start all over again. Of course spending extra money to turn an expensive hardback into a cheaper paperback does go against the grain. But if you’re never going to sell those hardbacks then they aren’t expensive assets, they are expensive write-offs. If you can make more off them than you could as a remainder, then you are doing a good thing. In academic publishing this is done rather more often than you might think.
The production costs involved are: whatever inventory value you are showing in your books, plus the freight cost for hauling the inventory to the bindery, the cost of printing covers, converting the books to paperbacks and shipping them back, plus of course some spoilage allowance. When the books reach the bindery the jackets get taken off and thrown away. Then the spine of the book is guillotined off and the cover discarded. You have to design and print a paperback cover — probably the design will be the same as the jacket so it’s just a matter of adjustment, but it has to be done. The denuded book block is then bound in the covers and trimmed as it comes out of the binding line. Your paperback will end up somewhat smaller than the hardback was. If the hardback edition was printed as a 6-1/8″ x 9-1/4″ book, it will deliver as a 5-7/8″ x 9″ paperback — 1/8″ is trimmed off the spine to remove the hardback binding, and then after paperback covers are applied the usual trim of 1/8″ top and bottom and foredge is taken.
These paperbacks won’t end up cheap: but if you can profitably get rid of some hardback inventory you’re probably ahead of the game. Trade publishers, who are used to dealing in larger quantities, would turn up their noses at this sort of thing. They’d find it cheaper to waste the hardbacks (or maybe remainder them, though that risks diluting the market for your paperback) and reprint the paperback anew.
You can always recognize one of these books. The endpapers from the hardback are usually there — it’d cost something to remove them — and if they were colored ends this will be rather obvious. But the real proof is the ISBN. The copyright page will carry the ISBN for the hardback only while the cover will have a different ISBN, the one for the paperback. (Of course if there were both hardback and paperback editions right from the start, this ISBN test won’t work.)