Rename with last day of month when source only contains year-month

The record is passed to the script
See the skeleton script below

on performSmartRule(theRecords)
	tell application id "DNtp"
		repeat with theRecord in theRecords
                                           <<< insert code
		end repeat
	end tell
end performSmartRule

I’d like to rename it to has the last day of that month

Here’s example code to get the last day of the month and rename the record

			set theName to name of theRecord
			set theName to theName & my LastDay(texts -6 thru -1 of theName)
			set name of theRecord to theName

on LastDay(theDate)
	set theyyyy to characters 1 thru 4 of theDate as string
	set themm to characters 5 thru 6 of theDate as string
	-- Convert to the first day of the following month
	-- Then get the previous day
	set NewDate to current date
	set year of NewDate to theyyyy
	set day of NewDate to 1
	set month of NewDate to (themm as integer) + 1
	set NewDate to NewDate - (1 * days)
	return day of NewDate
end LastDay