Which version of FA are you referring to - FA 2.3.25+ or 2.4RC1?
In FA 2.4RC1, the following new defines have been added:
//
// Depreciation period types
//
define('FA_MONTHLY', 0);
define('FA_YEARLY', 1);
...
// Manufacturing types
//
define('WO_MATERIALS', 2);
...
// Tax calculation algorithms used in als and purchase (depends on supplier's invoicing software)
define('TCA_TOTALS', 1); // taxes are calculated from respective net totals for all lines
define('TCA_LINES', 2); // taxes calculated for every line, then summed
//
// Bank account owner types
//
define('BO_UNKNOWN', 0);
define('BO_COMPANY', 1);
define('BO_CUSTBRANCH', 2);
define('BO_SUPPLIER', 3);
...
// tax register type
define('TR_OUTPUT', 0); // sales
define('TR_INPUT', 1); // purchase
...
Quite a few settings in the config.php have been migrated to the sys_prefs table on a per company basis.
You can possibly check the (ST_CUSTPAYMENT && ST_CUSTCREDIT) in your constructs without touching the include/types.inc file.