Scripts for beginners.

Hello. The question is this: I need the hero to have a static army. That is, at a certain point, you are given, for example, 10 units of X and 5 units of Y. At a certain point, if there were losses, the army of that hero should be reset to the values of 10 units of X and 5 units of Y. Also, there should be the possibility to change the parameters, for example, a little later, you will be given 15 X, 9 Y, 3 Z. It is probably easier to create a function for "issuing an army" and place a trigger at certain points. But I will figure that out myself, but how to check the army, the hero, or whatever needs to be checked, and how to write a function so that it does not "add" units, but "changes" their values? Thank you in advance.