How can I change my voice over time?

No, you're just going to damage it, especially if their voice is out of your range. Imitation will only have you pick up on their accent and how the pronounce certain words. A speech therapist would be the way to go if you truly want to accent things different. I lost my speech in 2008 and while I was relearning, the doc was from Georgia, so I picked up on her accent over time. You're not going to change the timber by listening