A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
There is an old ruling on this topic here: viewtopic.php?f=59&t=65266&p=838845&hilit=family+library#p838845 but the rules on required targeting have since been changed.
Can I now use family library, fail to discard a dynasty card when instructed to do so by the first sentence (because I don't have one), then continue to resolve the rest of the action, placing a personality face-up into the empty province?
There is an old ruling on this topic here: http://alderac.com/forum/viewtopic.php? ... ry#p838845 but the rules on required targeting have since been changed.
Can I now use family library, fail to discard a dynasty card when instructed to do so by the first sentence (because I don't have one), then continue to resolve the rest of the action, placing a personality face-up into the empty province?
It's not that the Rules have changed, it's that Family Library's text has changed, so that the card in the Province is no longer targeted.
So yes, you can use it as you describe.