Hi,
If you become VAT registered during a tax year then the difference for VAT will be that you will need to charge VAT on your supplies of goods/services but you will have an entitlement to recover VAT on your purchases as input tax.
You can also reclaim VAT on purchases made before you become VAT registered on condition that these purchases were made for your business. You can see the guidance here:
Introduction to input tax
However, if you are looking to see how this will effect your Income Tax then you would need to contact our Self Assessment team;
Self Assessment: general enquiries
Thank you.