Changing the locks is most likely not the option you want to pursue. In at least some states changing the locks would fall under an illegal eviction. The only circumstance I know of where this would be acceptable would be in the case of abandonment. I believe this requires that all of the personal property of value has been moved out of the house by the tenant. I have only dealt with abandonment once, and that was in the state of Michigan. My lawyer advised me to move forward with the standard eviction process because of the sheer volume of personal belongings that were left behind.
Let me start this next part with, you don't want this to happen. If the status of your home changes by way of the town or city, a 24 hour eviction is possible. In some areas the water shutoff can trigger a condemned status with the city or town. This becomes a health and safety issue and can require a 24 hour eviction. I've had a similar circumstance occur in Michigan back in 2006. This is a special case, but you DO NOT want to pursue this avenue as it is FAR more trouble than it is worth.
If it were me, I would move forward with the eviction process you have already started. As always consult your local landlord tenant attorney on matters like this. It is better to protect yourself and lose a couple of days in the process than to go through an illegal eviction case.
One more thing. Another landlord I know has had success with cash for keys. If you need to get into the property sooner, this might be a good middle road.
Good luck,
-todd