The way it works with Kodi and the passwords file is with path substitution. When you add a new source that is smb and add a user/pass it adds the path in sources.xml and then it makes a passwords.xml where it does a from/to that changes <path> to user:pass@<path>. You can setup a new share which would make this passwords file again or just manually create it on your own via ssh
nano ~/.kodi/userdata/passwords.xml
and the contents would be an edited version of this
<passwords>
<path>
<from pathversion="1">smb://192.168.254.201/</from>
<to pathversion="1">smb://User%20Name:password@192.168.254.201/</to>
</path>
</passwords>
The %20 takes the place of a space if you happen to have one in your username. The username and password are separated with the colon. You would of course replace the ip address with your own or computer name. This MUST match how your existing sources are setup. If you have more than one path you have to configure you just add more <path></path> sections. It works the same as what I outline in this how-to for a different type of path substitution.