I think it will be usefull to make method to change user/reseller password by API call.

It's normal that changing admin password by API is very risky so just user/reseller should be ok.

You can already do this with the existing API.

I'm sorry but I really can't find how to do it in XML API documentation.

http://www.centova.com/docs/cast/CentovaCast%20-%20XML%20API%20Documentation.pdf

Looks like it doesn't explicitly mention it as an option in the API reference but it's valid to pass adminpassword to the reconfigure method just as you can with the provision method.

Make sure you fetch the account with getaccount first, then change the 'adminpassword' field, then pass all the settings back to reconfigure.

SOLVED
Thanks