I'll try to do it as you suggested tomorrow, and if any questions arise, I'll let you know.

Added 13 hours and 43 minutes later
So, I tried adding all the heroes to all the maps today. First, I opened a random map in the editor. I saw the editor for the first time in my life, and naturally, I didn't understand how to do what I needed. Then, I opened the mod with WinRAR. There's a folder called Maps. I was happy, thinking it would contain something like a list of default maps, and all I needed to do was add new maps to that list. But it all consists of a set of folders with a letter and a number in the name, for example, L1, which contain files with the same names. I was a little confused by this method. Maybe you could give me some advice on how to do this best and where to click.