Companies safeguarding their own interests

I received an email confirming my shift booking. However, it also stated that:

"Occasionally you may work shorter or longer hours than you were originally booked. In the case that this happens, you will be paid for the hours worked on the day."

Now imagine the situation was reversed and I was the one confirming accepting the shift but also stating:

Occasionally I may work shorter or longer hours than I was originally booked for. In the case that this happens, I will adjust my invoice for the hours worked on the day.

How do you think they would have reacted?