It is of historic value only. When Israel accepted Resolution 181 and borders as defined by 181 the Balfour Declaration became Null and Void. If it is found legal then people might start resurrecting the Peel commission that jews rejected. Military rules say to obey the last order given. Resolution 181 was the last order given. It became binding when Israel accepted borders defined in Resolution 181 on taking Sovereignty. These are the borders Israel was internationally recognised on as a Sovereign State.
Saudi king to meet with Obama on Friday amid Gulf concerns over Iran deal (Reuters)
from the article: Is the Balfour Declaration still relevant?