Format cell as drop-down list if another cell contains certain v

Hi there, I'm looking change the format of one cell to a drop-down list, based on the contents of another cell.

I've currently got a IF statement that automatically fills a number of output cells with either 'Yes' or 'No' depending on what is entered into the input cell (AB1). Here is my IF statement:

=IF(OR($AB$1="Role Fit 1",$AB$1="Role Fit 3",$AB$1="Role Fit 5",$AB$1="Role Fit 7"), "Yes", "No")

Now I also want the option to enter "Custom" into the input cell AB1 and then be able to manually select either 'Yes' or 'No' from a drop-down list in each output cell.

So in addition to my current IF statement, if AB1 (the input cell) contains the text "Custom", I want cell AB2 (an output cell) to be reformatted as a drop-down list with the options of 'Yes' or 'No'.

Please could you advise me on how I can achieve this?

Many thanks,

Harrison