So far as I can see, your council is already required to have met the transparency requirements in relation to the financial year 2014-5.
Although it sounds rather impractical, it appears possible that a council can alternate between being "smaller" and not. It isn't clear that the government figured out how this would work in practice.
Certainly a council can decide which side of the boundary it lies by manipulating its income and expenditure, although this would seem a highly irrational way to decide a budget. Yes, the audit or transparency arrangements will only be certain at the end of the financial year. Just how a council should behave during the year when it is close to the boundary is unclear.
I wonder why the council wants to evade the transparency requirements? They aren't really very onerous.