Providing that you dont earn over $1700 in a fortnight then you wont loose the pension altogether.
When working report fortnightly earnings to centrelink and they work out FTB A/B etc. You should look at taking out a percentage of your payments as tax as PPS is a taxable income.
CSA wont allow you to put in an estimate for increased earnings they will only take an estimate for a decrease. So you will have to wait until such time as the new financial year comes around and then they will assess you based on tax income records.