Because once you've adjusted it it isn't the same one anymore.
I see what you mean though. Even if you are trying to save it again to the same name, as soon as you type the name it changes the setting to that named setting.
The only way I can see is to delete the preset before you make your changes and then save it again to the same name. Or give it a temporary name if you have made many changes then delete the old one and rename the new one?
Definitely could be easier.
Carl.
