The admin side was a pain for us as most of our clients pay us by monthly standing order. What we found though was the decrease didn't cause too much of a problem - clients like having reductions - but going back to the original amount looked like an increase even if it was only the VAT. It made the clients look at the contracts in place as they were often referred by the Accounts Department for authorising. Luckily all of our clients authorised the increase, but we didn't like having to make our clients do the extra paperwork the changes caused.