Writeback Table - make field editable or calculated based on another field

Is it possible to have a filed be both editable or calculated?  

For example, I have an entry type dropdown column that can have Option 1 or Option 2.  If Option 1 is selected, I would like my Amount column to be editable so a user can enter an amount.  If Option 2 is selected, I would like the Amount field to auto calculate based on the values in 2 other columns OR no longer be editable.  I can do the calculation in the backend.

I have tried putting an equation in the Editable IF field but am not having any success.  I have tried many variations of If(Column(3) = 'Option 1', 1, 0)

Any help would be appreciated.

Thanks!