How can I apply settings to lowest level category

[GateKeeper]

I want to make mass changes using the "apply these settings to all children". Is it possible to apply changes to lowest level categories only?
Is it possible to apply only the changes made in the form, not all of the settings?
Is there something that describes how this option works and what it actually will do? I want to apply changes to the categories that are currently set to allow ads to be placed, but parent categories do not allow posts. If I want to apply the changes to the lowest level, I presume I have to apply this change to at least one child within the same parent category and that will propagate only to the other children within that same parent?
I have 4100 categories that allow ads and 1700 parent categories. If I understand this correctly, the best I can do is make the changes in 1700 children and apply that change to the other children that have the same parent. This would mean I have to do this 1700 times? Can't I just wiggle my nose!?

[Chuck S]

The apply to children works to apply certain permissions to children cats yes but only certain things

category thumbs or private is not set from parent but everything else should replicate

[GateKeeper]

Considering the impact of choosing this option, could you tell me please what is included when this option is checked. It will be important for me to know this before I go and apply a mass change like that.
For instance:
Contains Ads: If the child is currently set to "Yes" and the parent "No", and other items are changed, e.g. permissions, on the parent form, does the Parent's setting for Contains Ads propagate, or is that not changed since it wasn't changed on the parent and only the changed permissions propagate?

Thank you.

[Chuck S]

Basically thumbs and parent are the two variables that do not get changed so Contains Ads or the Parent Category stays the same every other thing like cat perms etc are copied to all children.