Hi,
1. I can't edit Kam maps with krom's map editor and save them. Why "saving map has been disabled"?
There are two reasons for this:
1. Some data used by the editor (terrain edging) is not stored in the original maps so it is difficult to edit them anyway
2. It was thought unethical at the time to allow the editing of the original KaM maps.
You can edit most fan made maps or maps that you make with the editor. (this might change and saving might be allowed soon)
2. Though it is not about map editing, i write it here. Is there any way to change the list(or program) which is used by AI to build its town? The way it does it is so stupid,
No. That is hard coded into the executable and cannot be changed. You can make it a little better, see bellow.
And the 3rd, the worst.

Why each time I make a map using Krom's map editor, AI builds only small town on created maps(about 10-12 buildings) or does not build at all. There are only 1(!) woodcutter's, lumbermill, farm, swine farm, mill, bakery, weaponsmith ect... stupid AI...
There is a solution for this. What program are you using to edit the mission files? (.DAT) I will give instructions for my editor, (KaMEdit-0.9) if you are using a different one then let me know and I'll tell you how to do it there.
When you select the AI Auto build mode, you can choose No, Yes or Smart. In Smart mode the AI will build a bigger town with multiple woodcutters etc. It still isn't perfect, but it is a lot better than normal if you want a big town.
As for not building at all, this is probably just a bug of KaM. (TPR) I've heard that if you save the game and re-open it then the AI often stops building. I think I've also heard that if something disturbs them then they never finish building. (e.g. you kill one of their labourers)
Hope this helps, let me know if you have any other questions.
Lewin.