Resources - Changing the hiring cost of creatures.

HOWEVER, this raises a serious problem when - UPGRADING creatures from one tier to another (in the original game, such an action costs a very symbolic amount in gold), here everything will be completely different. For example: one red dragon (RD) cost 3 sulfur and 3 crystals when hired, then you suddenly decide to transform it into a black dragon, which costs, say, 6 mercury in resources, and what do you think, will you pay the difference of 6 mercury for this (in reality, you won't, but more on that later), and will anyone return the 6 units of other resources previously spent on the RD? No, they won't. In the end, you will pay twice (yes, yes, just like how Russian banks work with loans, you take out a loan for an apartment, and after 10 years you pay for it as if it were two apartments). The same "flaw" will apply if one of the upgrades requires only gold. It will be IMPOSSIBLE to upgrade a "resource-based" tier to a "gold-based" one without losing what was previously spent. And that's not all. This same "trick" with upgrades can be used as a bug for selfish purposes. That is: we buy creatures at their original cost (in gold), and then upgrade them to "resource-based" tiers, for which no resources are charged from you anymore. This is a clever trick, but it cannot be fixed with a mod, as I then understood that such things are already embedded deeper in the game's code, to which ordinary mortals have limited access.