Slitherine

Steps:
In editor, user adds several units of a given type to the scenario.
User adds a trigger, set to execute at the start of a specific game turn, and uses the Change Unit Type effect, with a target unit selected, and new unit type selected.
User saves and launches scenario

Result:
Regardless of whether "Replace Original Type" is selected or not, function appears the same. The label of the button (Replace orignal type) would suggest that all units of the same type as the target unit would be replaced, but that does not occur. Only the target unit's type is replaced.

The "Replace original type" checkbox means the unit's original type is overwritten. I can't remember exactly what we needed this for - I think it was to turn Japanese Infantry into "Banzai Infantry" permanently, because by default Banzai Infantry automatically reverts to the original type (default infantry) at the start of a new turn. By overwriting the original type, they stay in banzai mode forever.

It is not inteded to affect any units other than the one you specify.

Ah, thank you very much. Now I understand.