If you open a drawing for editing (i.e. then save as a PLN) before including in your model (by hotlink or whatever) it would be great to be able to add a prefix upon opening....could not do it up to 12 - yet to try out 13...
rtw is correct that if you xref you can get a prefix to the Layer name. You could always add a standard pre-fix to the front of your layering system to try to clump your Layers together ( ie aa_ )