where are API variables stored (per domain values and default values)

Does anyone know where the values of the API variables are stored (per domain and the defaults)?

In various DA scripts there are references to variables enclosed in the pipe character

e.g.

|HOME|

and for example in this file
/usr/local/directadmin/data/templates/user_prefs

there are the following variables

|required_hits|
|rewrite_subject|
|subject_tag|
|report_safe|
|blacklist_from|
|whitelist_from|

Where are these variables stored
- per domain
- defaults

Are they stored in any editable format?

I really would like to be able to change the value of these stored variables programmatically.

Actually I am more interested in how to find where the "default values" are stored.

I found the per user values (applies to all this users domains) of
/usr/local/directadmin/data/templates/user_prefs
are stored in a text file
/home/username/.spamassassin/user_prefs