If it's in decent soil to start with you dont need to change it. But if it's been in the pot for 3 years it's likely to be rootbound. You may want to divide it or put it in a larger pot.

If I divide It do you think I could grow a piece in a bonsai pot about 2.5 inches deep L14 x W8 inches

Two points:
1. When you "change the soil" of any bamboo, and you are not dividing the plant, you will get your best results if you use a larger pot, disturb the rootball as little as possible, even if it's rootbound, and simply re-pot. You could use the same size pot if you take a division, put the remainder of the plant back in the old pot, and add new soil to fill the pot.
2. I'm skeptical of whether the bonsai idea will work very well, unless you have a very small culm that can be sustained by a very small rootball. For the mature plant you are describing, I suspect that taking a piece of rootball only a couple of inches deep will make it hard for the new division to survive. You can try, but don't have high expectations.