Edit Invoice which has been accounted for on VAT return.

What is the impact on the VAT of editing an invoice that has been previously accounted for on the return, but NOT paid. I need to alter the VAT. Will this adjustment come through on the latest VAT return as a -ve and +ve depending on the net adjustment.

So just to be clear. An invoice was entered without VAT. The total invoice value is 120. Now I need to edit this to include the VAT. i.e.. 100 Net and 20 VAT. This was entered say in Q2 2014 and included in that quarters VAT return. I am now in Q4 2014 and about to do the VAT return but need to know if the Q4 2014 VAT return will adjust through. Also will I lose my VAT reconciliation for Q2 2014 if I make an adjustment ?

The other solution is to VOID and reinput - but this is painful.

Thanks