Paying per hour and changing work hours

Q: We at a school employ teachers who are paid per hour. Working hours are fixed by the administration. Can their working hours be reduced in the next year without their consent. E.g. a teacher started work in 2018 and he was given 4 hrs teaching. 50 rands a hour (2hrs in the morning and 2 hrs in the afternoon.

1. In 2019 can we reduce his working hrs to 3hrs a day without his consent. In other words his work and salary will be reduced.

2. Can we impose on him to teach more hrs e.g. 5 hrs and pay him accordingly.

Wiping semen

Q: When my semen discharged from the place and some of it fell on my room mat but instantly I cleared the dirty place with a cloth. Now I'm confused, shoud I wash that particular place which got affected by my discharge or shoud I wash the whole mat?