I can't really help much with your question regarding multiple selection, but regarding setting the single popup choice to "Not Applicable", which I assume you mean that you don't want the use to bother with any interaction? As a user interface choice, would it not be better to disable the popup all together? So bind a boolean value to the 'enabled' property of the popup then just set that value within your if / else....
on setTheDays_(sender)
set typeFlag to theTypeStore's titleOfSelectedItem()
if typeFlag as text is in {"Once","Monthly","Yearly"} then
--theDayStore's removeAllItems()
--theDayStore's addItemsWithTitles_({"Not Applicable"})
set my blnPopupEnabled to false
else
set my blnPopupEnabled to true
set tempString to {"Every Day","Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"}
set typeFlagDay to theDayStore's titleOfSelectedItem()
if typeFlagDay as text is in { "", "Not Applicable"} then set typeFlagDay to item 1 of tempString as text
theDayStore's removeAllItems()
theDayStore's addItemsWithTitles_(tempstring)
theDayStore's selectItem_("Monday")
theDayStore's selectItem_("Friday")
theDayStore's selectItem_("Sunday")
theDayStore's selectItemWithTitle_(typeFlagDay)-- Even with this removed, the above statements do not work
end if
my setTheMonths_(sender)
end SetTheDays_