Hi, welcome to the Spine forum! Have you read the page of Skins in the user guide?:
Skins - Spine User Guide: Skins
Create a skin placeholder for the braid, attach a braid region or mesh attachment in the skin placeholder for skins that you want to display the braid, and leave the skin placeholder empty for skins that you do not want to display the braid. This allows you to switch between skins with and without braid depending on the skin.
Note that as you have noticed, the state of which attachments (or none) are displayed by each slot is shared among all skins. This allows the same animations to be diverted even if the skin is changed, e.g. different eye images can share the same blink animation.