Although the EU VAT regime will remain in place until negotiations between the UK and the EU will be concluded, it is most likely that new UK VAT legislation will come into force in the spring of 2019. It seems you have enough time, but I highly recommend to anticipate on these law changes as soon as possible.
Mandatory test cycles In order to implement Brexit, SAP settings have to be changed. From an operational perspective processes and controls of companies have to be updated to the new situation at hand. SAP must reflect these changes which means that tax determination logics, tax codes, invoice and reporting requirements have to be assessed and the new rules should be implemented.
Besides assessments by the tax function, a considerable effort by the IT department is required to implement Brexit. Change management processes follow strict IT policies and specific and extensive test rules apply before changes can go to the ERP production system. Those mandatory test cycles are time consuming and have a huge impact on resources.
When manual processes and controls are set up to manage complex VAT transactions that include dealing with the UK, new guidance should be drafted and ongoing review should take place to check if these new procedures are actually complied with.
A thorough and effective preparation should include a stakeholder analysis and the development of a SAP roadmap for change. This will provide insight into the work effort and the amount of time and money that you’ll need to invest.