As you can see, the rules FORBID weakening non-upgraded neutral armies... That is, regardless of the reasons, they cannot be weakened.

But, as you can see, AmberSoler misunderstood this when reading your rules, because you don't emphasize there that this prohibition doesn't allow for any reasonable explanations or exceptions. Now, I hope he understands that in your tournaments, you cannot retreat from a mixed army if, during this attack, the stacked unit was not completely destroyed. That is, no reasonable explanation for weakening will work. Even if you leave this weakened mixed army alive until the end of the game. Is that correct?
P.S. However, I understand that in AmberSoler's tournaments, this rule will be worded differently?? In AmberSoler's rules, it is implied that sometimes, if the TRUE MOTIVATION for weakening a mixed army convinces with a reasonable explanation that you don't need to weaken the army, but simply need to retreat to the Fortress, then such an exceptional action is PERMITTED. This is where the discrepancies in the rules arise, when in some Heroes 3 tournaments we read one thing in the rules, and in others - something else.