Variant Modifications was a game mechanic developers planned to add and be worked on after 2.0, but the idea was later scrapped. Variant modifications would have given the tank an upgrade to a different variant/mark. This was purely changing the tank‘s appearance. It is not known whether this was to be done automatically upon a chassis upgrade or purchased separately.
Here is the list of tanks that were to be modified.
AMX - 30
AMX - 13