Updating Language constants dynamically

[DrByte]

Can you clarify the difference between the language files and the database configuration table, in terms of which one over-rides the other? If I changed the values in the database - are they reflected through the site or are they over-ridden by the language files?

Neither.

The language definitions are not contained in the database.
The configuration table is used for configuration settings, not language content.

[DrByte]

If I want to do this without affecting security, is there a method of achieving this?

Yes -- use the database alternative we've been discussing:

I think an alternative may then be to set up the new defines to be canged to be changed in the database directly, and should I require to add custom defines then I can just add rows to the database tables where necessary / create a new custom table.

If you want to rewrite the language infrastructure to use the database instead, keep in mind the need to support multiple languages and also to handle code upgrades. You'll still need to create a user interface to present and collect the information, then validate it and save it.

[DrByte]

Do you know if the values are usually taken from the database first and then placed into the files or are they never 'syncronised' and if not which values are taken as being the 'main' ones the database or the language files?

It all depends how you write your custom code.

A constant is ... well ... constant. It never changes once defined. So, whatever you set it to be, it will be. You can't change it later without loading a new page.