You can, but it wouldn’t be a wise move, for two reasons.
Firstly, having an unpaid balance transfer means you won’t qualify for interest-free days on purchases. This means you’ll pay interest from each purchase transaction date until the purchase transaction is repaid, at the credit card’s ongoing purchase interest rate.
Secondly, any repayments you make will be allocated first to your new purchases balance, because it attracts a higher interest rate than the 0% on your transferred balance. Only when the purchases balance is cleared will any of your repayment be applied to the transferred balance. This could prolong the time you need to repay your transferred balance, putting you at risk of incurring the high revert interest rate.
