Where did you read that it can only change with a formal agreement with Palestine and Israel ?
The Jewish State
"(b) A Jewish State called Israel exists in Palestine and there are no sound reasons for assuming that it will not continue to do so.
Boundary determination
"(c) The boundaries of this new State must finally be fixed either by formal agreement between the parties concerned or failing that, by the United Nations.
1949.I.13 of 31 December 1948
Please try to keep up.
Interesting. Now read my question again, becasue you didn't answer it. I asked about land, not boundaries