Currently
<Cost> <Resources> <food op="add">-25</food> <metal op="add">25</metal> </Resources> </Cost>
is set in dozens of unit templates, all of which have the Mercenary class. (A few other templates have the Mercenary class but not those lines, but those are all champions). This patch introduces a new autoresearched technology, similar to advanced_unit_bonus.json and elite_unit_bonus.json, to set those cost modifications in only a single file, which means fewer unnecessary lines in the templates and less work for future additions or changes.