[Imp]

Follow the above advice then try those nations.
However it is quite simple if your not confident copy the whole MBT folder to another one.
Create a shortcut & rename it backup or whatever.
Use this copy to try modifying so your original install is safe.
Misc tab > turn Show ID Numbers ON #
Utilities tab > Mobhack OOB editor > Formations
Select the correct OOB > Press open & swap the tank ones for something different.
Save any changes after you make them.

# You can turn it off after this just shows the ID number of the formation/units.
So if the tank formation is ID 20 you just scroll to ID 20 & change it.
its fairly straight forward & if yo cannot figure it out just delete the backup installation.