President - most practical on the line stuff is never written down because no one wants to be held accountable when it goes pear shaped. Boeing writes "advisory" for this very reason.
It is always down to the commander of the aircraft to be satisfied he has complied with the legal minimum performance for his aircraft, that will be the answer you will find in any legal document.
Now, if you was tight on the performance by a 100-300kg then checking the performance would be a good idea. If you have 2000kg then a small change wouldnt change the RTOM by much.