As part of the Government’s July Jobs Stimulus, the standard VAT rate of 23% will be temporarily reduced to 21%. This will come into effect from the 1st September 2020 and stay in place until the end of February 2021.
The Revenue have a guide on how businesses should deal with VAT rate changes, which you can find here. One thing to highlight from the guide is if you are sending an invoice to a VAT registered business the VAT rate that should be applied is the rate in force at the time of issue of the invoice. If you are sending an invoice to a non-VAT registered person the VAT rate applied on the invoice will be based on the date the goods or services were supplied, not the date of the invoice.
From an accounting point of view most systems should be able to deal with a new rate of VAT. I would suggest adding a new VAT rate as you will need to revert to the 23% from the 1st March 2021. For businesses who pay VAT on a receipts basis you will need to make sure your systems are tracing the VAT back to the invoice and not the date of the lodgement.