I think some things you are looking for are hardcoded (e. g. status interactions). The status stats are in the Potion.txt/Potion.xlsm files in Data\Editor\Templates\Stats\Main\ and ...\Stats\Shared\ and their subfolders. A few more options to change stats can be found in the magical Data.txt/Data.xlsm file in ...\Stats\Shared\ ; I really wish there was more in it!
With 'special event scripts' you probably mean the Base char script. Beside Potion and Data this is the third option I know of to modify or add a status: a lot of things are possible with char scripting. Unfortunately the most important functions to handle potions (a new status for example) are partly broken or incomplete. Some more information about the potions problem related to char scripting can be found here:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=581127#Post581127 (number 9 and 17 and the following information from Baardvark who had a hard time with Potions).
For more information just ask. I'm sure some of the other active modders will answer your questions, too.
