Thanks everyone for your input. Much appreciated @poncho1234 and @apmuthu.
Maybe we should be able to create a VAT with dates attached to it.
Lets say that we have a start date and end date for 14% VAT and then create new VAT for 15% with new Start date and end date some date in future untill new VAT rate is created.
I think that people with line item vat per stock item would have a nightmare. Depending on the number of suppliers and clients could also be time consuming.
I will make a copy as a training database and then play around with it to find the best solution for each client.