Would it be possible to get some of the existing order of 805 or 807 if they are ordering them. Not taking over the order, but the build sequence swapped around so a few are made for Grand Union before the final ones for current order delivered.
If it is just interior spec that differs, and bodyshells, bogies and all the powered bits identical then not impractical unless the current orders all needed by certain dates.
I am thinking back to the desiro fleet, Angel ordered 25 dual voltage units speculatively, 3 were built, next 19 were converted to become part of SWT class 450 order, other 3 got moved to back of build queue and became part of subsequent order. The AC equipment already ordered ending up on 350s or 360s. So not like hasn’t been swaps between ordered batches before.