At any time can I pay off the balance or make larger monthly payments

you can schedule payments whenever you want.. and you select the amount.. I don't think any credit card would limit the amount of your monthly payment. What's really nice about the Apple Card is that they clearly display what you need to pay in order to not get interest charges.

Or... Are you talking about installments on your Apple Card? if so, then yes, you can pay extra each month, but you cannot change the amount that gets auto deducted. You'd have to manually pay extra each month. But installments are interest free, so I'd just pay the installment amount personally.