Reapply UK visit visa, can I change some data?

In the application question about " how much you earn each month after tax? In the 1st application we declared Php 10400. That is from Php 400 (daily rate) x 26 working days, and we explained that my sister is exempted from tax since she earns minimum wage. But we forget to include the 1500 allowance she receives every month, because it was not stated in her payslips.

Now, we plan to correct this in the second application from Php 10400, we will declare Php11,900, that amount is from 10400+1,500 allowance the company gives, since in the salary received certificate allowance is included.

The main ground for the refusal was the proof of salary received since she doesnt have bank statement since they receives cash payment, and now we are providing salary received certificate from the company.

My question, would it be fine to change the declared income after tax each month? And would it not be another ground for refusal?

Thanks a lot. Waiting for advice.