Some flavours work best re-distilled (eg. juniper), some work well simply soaked in the finished spirit. Vanilla is great without re-distilling (spiced rums are done like that), but I wouldn't have a clue for peanut butter (it's not high on my list of flavours to try in spirits). My guess is that the oils are going to be problematic.
As Doug's already said, no point adding botanicals during a reflux run (it strips flavours) unless you can somehow add it to the vapour as it leaves the column before condensing. It's more common to make your neutral, then run it again in pot mode through/with botanicals.