>>Is the install.xml file for (eg) Wordpress viewable on this site or do I have to subscribe to download it?
You can access the file on your server at:
/var/softaculous/SCRIPTNAME/install.xml
or you can go to the install form and you can view the source from the browser.
>>Essentially I want to be able to specify at the time of installation:
You can write your own code to pass these details such as :
Table prefix
Admin user
Admin password and other fields except :
Mysql host (if not localhost) IP and port
Database
Database user
Database password
during the installation time.
Please let us know if you need any further information.