if you have registered for VAT while under the threshold then
(a) you are entitled to reclaim VAT on inputs and
(b) you are obliged to charge whatever VAT rate is appropriate to your outputs/sales.
You cannot selectively decide to claim VAT on the purchases and not then pay VAT on the sales.
If you registered while under the threshold solely to claim VAT on the purchases then you may have made a bad decision, especially if your customers are largely non-VAT registered persons.
Additionally, if you seek to de-register while again still under the limit and have reclaimed more than you have paid in VAT then you cannot de-register without repaying the excess you got to Revenue.