Since synced layers are often used to sync together two smaller parts of the same part of a rig, the artwork in layers that are synced together is often intertwined. Hence, it can be useful to edit the artwork in two or more layers that are synced together simultaneously.
Several of the drawing tools in the Tools toolbar have a mode specifically made for that purpose, the Apply to Synced Drawing Layers mode, which can be enabled in the Tool Properties view. When this mode is enabled, your drawing tool will have affect the currently selected layer as well as any layer that is synced to it.
This mode is available for the following tools: The 
Select tool, the 
Cutter tool, the 
Reposition All Drawings tool, the 
Pencil Editor tool, the 
Edit Gradient/Texture tool, the 
Eraser tool and the 
Paint tool.
How to edit synced layers
- Make sure you are using the Camera view and not the Drawing view.
- In the tools toolbar, select either the Select tool, the Cutter tool, the Reposition All Drawings tool, the Pencil Editor tool, the Edit Gradient/Texture tool, the Eraser tool or the Paint tool.
- In the Tool Properties view, there will either be an
Apply to Visible Drawing Layers button or an 
Apply to Synced Drawing Layers button:- If there is an Apply to Visible Drawing Layers button, click and hold on it and, in the pop-up menu, select Apply to Synced Drawing Layers.
- If there is an Apply to Synced Drawing Layers button, click on it to toggle it on.
- If there is an
- In the Camera view, your can start using your drawing tool. It will affect both the current layer and its synced layers.