There seems to be a tacit understanding of 250/10,000' not applying to all long range jets. The controllers understand it can't be done. On the incredibly rare occasions we have been asked to keep speed back, we've replied 'unable 250kts' or delayed flap retraction. There has never been any querying. They know your requirements speedwise.
Height restrictions can be for noise abatement or traffic patterns nearby- it is irrelevant why to us. Whatever the reason, it is down to you to not infringe them or give adequate warning you are unable to make them. Unless you are right up to max weight with unfavourable winds, there is not likely to be a problem if you delay flap retraction until you are sure you are going to be OK.