Skippy,
I spoke to RAA today, and the E24 rego can be reverted back to 24, if the engine was replaced. So a scenario like this....
At TBO, I apply and get issued an E24 rego. That allows me to continue running on condition. Then, 3, 4, or 5 years later (or whenever) me or a new owner can simply put a new motor in, and revert it back to 24 Rego - PROVIDED that any other mods done are approved by Evektor (Glass etc). If do those mods unapproved, there will likely be no way back to 24. Hence why I need their approval, or no glass gets installed.