Hello,
Yes, it is possible to customize the assistant. You will find simplified documentation on the GIT server at the following address:
https://git.tuxfamily.org/ostorybook/code.git/tree/doc/fr/wiki/function/Assistant.md
Unfortunately this documentation is not available in English at the moment. If you wish to translate it, it will be a pleasure for me to integrate it.
You can find an english version of the manual in th Documentation part of the site, but it is a bit out of date.