The solution is a bit tricky, but it definitely CAN be done. First, you need to create a custom calendar that shows only the last Thursday of each month as a working day. To create this calendar, first edit the [Default] item on the Works Weeks tab and mark Mondays, Tuesdays, Wednesday, and Fridays as nonworking time. This will leave only Thursdays as working time on the entire calendar.

Second, select the next upcoming Thursday that falls on the last Thursday of the month. Mark this day as a working day that recurs Monthly on the Last Thursday of the Month, and set it to recur for 25 or more occurrences. Then select the next Thursday that occurs on the first Thursday of the month. Mark this day as nonworking time that recurs Monthly on the First Thursday of the Month, and set it to recur for 25 or more occurrences. Repeat this process for the second and third Thurdays of the month as well.

Finally, look for months where there are FIVE Thursdays in the month, and mark the Thursday of the fourth week as nonworking time. You will probably need to make each of these an individual nonworking time exception.

Finally, apply this custom calendar as a Task Calendar for the T5 task and be sure to select the "Scheduling ignores resource calendars" option. From this point forward, the F5 task will always be scheduled on the last Thursday of the month. Hope this helps.