Subform Add Row any way to not Add Row based on a condition

Hi

in the add row script area of a subform is their a way to "cancel" the add row, say for example the user has entered some data which is the same as the row above, i can see how to alert them using a for each loop but i still cant stop them from adding the row

so something like if condition == (don't add row) or if condition delete last row added

thanks