The salt is a random 8 character value, it should be different for every password.
What I'm curious about is if then using some php code to change the password in the database, will that automatically be read by ISPConfig, PostFix, Courier, et cetera? Or will it have to wait on a cron job or need some sort of restart or trigger before it goes into effect?
For courier and smtp and ispconfig it is enough to chnage it in the database. If ispconfig will support other configurations which may need to change config files then it will not be enough to change only the db, in that case also a record will have to be written to the sys_datalog to start the server side processing of the changes.