If what you wrote is really mod, it may be that they edited wc3 itself.
I never done this before, but you could try one of the following:
a) use Spellbook ability (it's an item ability) and put into it the "Build Tiny xxx" abilities (e.g. Build Tiny Barracks ability found in item category).
The disadvantage here is that the unit will go to the place and the building will builts there by itself and that there is no transparent model showing that something will be build there.
b) add all buildings into the "Techtree - Structures built" for that builder. Even when they are not displayed in game (because there is no more place for them in the command card), the unit can still build those structures.
You could then add to the builder an ability - something like "Display advanced structures", etc.
When you click it that ability, you make certain structures unavailable for constructing for that player. This will cause those structures not to show in the command card. Since you have now space in command card, it will get filled by those structures that were out of range before.
When you press the ability again, it will return back to normal.
c) merge of a) and b) - Add all buildings for the unit by doing what I wrote in option b), create spellbook spell and fill it with "Build tiny xxx" abilities as I wrote in option a).
Finally, catch when building is being constructed. If it is one of the advanced buildings, remove it and instead order your worker to build the structure there.
Edit:
From the pictures it seems that those are not buildings but simply items in a shop. That is something a bit different.
