Hello,
You will need to modify the code of the logon form web part:
devnet.kentico.com/docs/devguide/modifying_the_code_of_standard_web_parts.htm).
In this web part (
\CMSWebParts\Membership\LogonForm.ascx.cs) there is a
btnPasswdRetrieval_Click event and you will need to change its code.
You will replace existing code with your custom password generation algorithm. This generated password will be sent via an e-mail using our
devnet.kentico.com/downloads/kenticocms_api.zip from this place as well (in similar way as it is described in the example for web part modification in the link above) and you will send the e-mail with appropriate e-mail template in which you will pass the new password (e.g. CMS.EmailEngine.EmailSender.SendEmailWithTemplateText(string, CMS.EmailEngine.EmailMessage, CMS.EmailEngine.EmailTemplateInfo, CMS.GlobalHelper.MacroResolver, bool)).
Best regards
Ondrej Vasil