Foreign currency bank accounts

If a non-domiciled individual elects under the extended SP10/84 practice to treat all his non-UK foreign currency bank accounts (FCBAs) as a single account how far does that deeming go?

That is does it just apply for the purposes of ensuring that there isn’t a FOREX gain when transferring between those accounts? Or does it apply for all purposes including subsequent remittances from those accounts?

For example FCBA 1 contains US$1 000 all of which is foreign unremitted income. FCBA 2 contains US$10 000 of capital.

$1 000 is transferred from FCBA2 to FCBA1 and in order to avoid a currency gain on this transfer the taxpayer elects under SP10/84 as extended.

Later the taxpayer brings $500 into the UK from FCBA2 (assume no further capital gain on this because rates have reverted to their original level).

The taxpayer believes that the $500 is...