Backdated voluntary VAT registration and final accounts

I note it is possible to backdate a voluntary VAT registration for up to 4 years.

Could someone help me by setting out the basic principles for the following situation.

Given that accounts for a non-VAT reg business are prepared in a different way - for example, purchases would go into P&L a/c inclusive of VAT; capital expenditure would begin its life at its VAT inclusive cost ...

If the business has been ticking over for one or two years and is subsequently VAT registered, backdated to include these earlier years, what are the implications for stock valuations, fixed asset valuations in the current years accounts?

Do the previous years accounts have to be amended, or can it all be dealt with in the current years accounts?