Can someone change their countenance?

As my wife says my expressions belie what I’m really like. Short answer is I look pissed off all the time. If I’m thinking, I look pissed off; if I’m concentrating, I look pissed off; if I’m frustrated, I look pissed off; if I’m pissed off, I look pissed off.

If I determine to be deliberate about it, can I change my countenance?

Has anyone had any experience with anything like this or have any suggestions?