There is an add on that does this from Andy B though @MorTuadh. I only found this out after we did our conversion to Xenforo a few months ago(which is a great system btw), and the addon works GREAT and helped us on the tail end but I wish I knew about it up front. The addons are from @AndyB , who has a tremendous number of addons available. For XF2 he charges $25 for as many of his addons as you want to use for a year I believe. It allows you to do two things----change a date and time of a post which allows you to naturally reorder them, and there is a second add on which allows you to change an author so if something didn't import correctly or as an admin you want to give credit to some else you can do so.