You can change the amount for outstanding mortgage balance. Since the 1098 instructions ask lenders to report beginning of year mortgage balance, but the tax return limits based on average, it is acceptable to adjust this figure, and doing so will not cause any errors.
Make sure you are using an allowed method to compute the average balance. If you had the same mortgage servicer all year, you can use the interest rate method. To figure this, take the total interest paid in 2024 divided by interest rate.