Can I kneel Old Nan to give a character that is not in play but in my deck the Maester trait at the beginning of the plot phase and then search my deck for it? Old Nan's text reads as "Any Phase: Kneel Old Nan to choose a Character. until the end of the phase, that character gains or loses a trait of your choice." That would be absolutely awesome.

No, unless specifically otherwise specified, cards can only interact with cards in play.

Thanks I was simply curious. Appreciate it.