In the above work pattern images you can see that the column for "Is Half Day" is set to false for all the days.
And now if you wish to change the employee from full time to half time than you need to make a change in his work pattern. So for that is the employee is coming only for half days for all the working days than you need to make the "Is Half day" column true for all days.
And for half day users you can create an event like "Holiday-part time" and then create a part time leave visibility group which would be visible only to user who are half day users.See below:
So now in the above image user "Vijayvergia Manju" would be having the privileges to apply for Holiday Part time.