Adjustment to Floreant POS

I am currently running the well known open source epos software 'Floreant'. I require a few minor adjustments to be made to the fundamental runnings of the software; 1- At the final stage (ticket closing) I would like a service charge of 10% to automatically be applied, but a pop up dialog box or otherwise to appear with the option to remove said service charge. 2- I would like an additional button to appear at the same stage with an option to apply a 'staff discount' preferably one that can be specified at the time of discount, alternatively a fixed 20% would be fine too. There are further adjustments to be made if these go well, and if the selected freelancer performs well, will of course get this additional work. Thank you very much in advance S Morgan