Check box functions

I have a cell (D19) that I want to be automated to return a value based on a formula (it will equal Cell D15). But I also want to have the ability to allow the user to override this and enter a manual value if needed.
My idea on how to do this is having a check box with a macro where if it is checked it will unlock the cell and clear out the formula and when checked it will reenter the formula and lock the cell.

Also same form - I need a check box that will check all applicable check boxes (all boxes under Deductions to be taken).
Can anyone assist me in setting up these check boxes so that my functions will work, or if there is a "better" way of providing these functions please let me know.

Thank you for your help!!!

Teresa