Changing the configuration

I initially made the SEF showing all categories, because that was the easiest way to handle many categories with the same name.

But for one section of the site, I want to reduce the amount of categories in the SEF, so I have an idea:
I delete the SEF's for this section, then change the configuration of Ace to only show last category, and then let it create new SEF's for this section based on the new config.

But what will then happen with the rest of the SEF's? Will Ace then recreate new SEF's for the whole site, or can it leave the SEF's that was created earlier?