Yes, it will break certain maps which use some of the natives from 1.29 and up. Blizzard could use their version detection to check which version the map was created on and force it to use the old behavior, but that means more code to maintain and it would cause odd behavior on people using 3rd party editors.
Somebody was asking also about GetUnitAbilityLevel
(and natives like it, I suppose) and whether or not it will return 0 for level 1 abilities. They currently still retain their old behavior which leads to inconsistencies, yet changing it will break tons of maps. That native is also used to check whether or not a unit has an ability. Level 0 means the unit does not have the ability. I'm thinking Blizzard should have left abilities at index 1 to keep it consistent with the old API. Maybe levels should be treated differently than indexes. For example we don't call SetHeroLevel(hero, 0)
to set a heroes level to 1, however we use Player(0)
to denote player 1.