General config.php question

[cheat-master30]

If you change the username and password used to connect to the database to a set user from the original one, does it affect the data currently in the database in any way? Because as usual, the host says to change the password for the 3rd time within a year, and I don't know whether just to update with the new password there, or use a minor user to connect to the database.

By the way, before anyone worries:

I have like 10 backups in order of date.
Various mods are installed
I even have a whole set of backup vBulletin files

I need to know whether it's wise to change the user it uses to connect to MYSQL.

Oh, and there's no problem with password security currently, as all passwords are random letters and numbers somehow remembered.