Unfortunately not. In the gameplay of Conan Exiles, cost reductions for crafting recipes come from benches. Upgraded benches like the Alchemist, Blacksmith, Armorer, etc can sometimes reduce the cost of crafting recipes. Hardened Leather has to be made at a Tanner's Table, and unfortunately, there is no upgraded version of that bench. The Tanner's Table that you craft in the early game is the same one you'll use in the end game, and thus the recipe for Hardened Leather is fixed. As I mentioned earlier, this is both a positive and a negative. You can't improve the cost, but it does make calculating how much of each resource you'll need much easier.