I think this may be relevant to me too... I think many small business change. For example the florist down the road has closed her shop and only sells on one market but mainly does weddings/funerals and corporate now. So she is doing the same activities, just more of one of them.
"If the balance changes but you continue to do all the same activities, carry on using the percentage that was appropriate at the start of the year until the anniversary of you joining the scheme. Review the balance between the parts of the business each year. Make this review for the first day of the VAT period in which the anniversary of you joining the scheme falls. If on that date the balance has changed, or you expect it to change over the year ahead, switch to the trade sector for the larger portion of your expected business.
This may also mean that your flat rate changes. If this occurs use the new flat rate from the start of the VAT period in which your anniversary falls, not just from the anniversary to the end of the period."