By default the Tool Palettes are located on your local drive. If you create additional P&ID Symbols and put them on your Tool Palette, you will be the only one having them on your Tool Palette, but your colleagues are supposed to have them on their Tool Palettes as well.
So if you think about creating your own P&ID Symbols you should start exporting your Tool Palettes and put them on a central network folder.
Before everybody now starts importing the Tool Palettes from the network folder you might think about creating your own Workspace and import your Tool Palettes to that Workspace.
Ex- and Importing Tool Palettes for AutoCAD® P&ID is no different than vanilla AutoCAD®. So if this is new to you just look into the AutoCAD® Help.