Those settings are client side only.
In theory Stratum server implementation should send those settings to clients as well as send work restart command as soon as a block change.
Those settings are defaulted locally by the respective miner, or set locally via command line or conf file. Just in case I was mistaken, I just ran through slush's stratum server source and couldn't find any relevant source that would transmit those settings to the clients. I did just work 12 hours though, I might have missed it if it was in there.
Mining clients do move on when they receive a new block message.