@Graham ********
i can tell u from multiple friends that isn't the case.
Of course it always comes down to "we were told" (not ur fault of course).
Different people, facebook members, Immigration officers, agents.... will all have a different answer.
The embassy letter is an extension of stay.
For what reason... doesnt matter.
Its a hard stamp that gives u evidence and proof of legal status.
I have many friends who used it cuz they needed an extra week or few weeks for their NON-ED or NON-O visas to come through.
The change of visa status goes under consideration for 2-3 weeks... so they applied to the 30 day extension w consulate letter... to buy themselves a month so they can sort the other visa out.
Anyway... just some ideas and info of people who did it.
If someone says they cant... for sure they won't. That doesnt mean someone else might or might not be able to do it.