BFGMiner (at least) will also send mining.suggest_target("hex target") upon connection, if the user has a preferred target.
Why would it do this?
There is already mining.suggest_difficulty(difficulty)
No, there isn't.
Nothing implements this, and it isn't documented anywhere.
If you say something that contradicts facts in front of your face, oddly enough, that just makes you look foolish.
Try a little sense in your posts.
One of the posts above, shows where it was documented, over a year ago:
https://bitcointalk.org/index.php?topic=108533.msg1543341#msg1543341Forum posts are not documentation.