Try this. Go to "Data" file, then "missions", then to "Battles" file.

From there copy any "md3" file you want to modify, and place it into the "Data/designed" file.

From here you can perform any modifications you want, and then copy and place back into the Missions/Battles file. click ok when asked if you want to replace.

Then it should work.

Let me know if this will not work,

Have fun!

Daddio

Then, do you think that they("Data" file, then "missions", then to "Battles" file) are related to units or buildings abilities in CAMPAIGN?

This is more complicated than it seems.

Unit abilities ( attack, defence,...) is modding and is done in the MD files.
Building abilities(cost is modding too and is done in the MD files

However, Building abilities such as producing times, for a mine for example, can be done trough the map editor with the help of the 'additional settlement information"- upgrade section, where you can change the effect of an upgrade for example which influences the producing times/amount.

It all depends what exactly you want to do.

Changing existing campaigns can be very tricky aswell, because a lot of units and buildings have additional information attached to them and deleting them or changing them may cause the links to the script to malfunction if these are not changed aswell and cause unpredicted results in the campaigns/scenario's. Often a crash to desktop.

Read , try out and ask specific questions.

It is far to much to write out a comprehensive guide on changing/setting up scenario's.