—–> 1) You will need to make sure the template_notices hook is in your template.
—> how to add it in my template if does not exist
—–> 2) I’m not sure if an email is sent on settings change by default, but if not, the general approach would be to hook a custom function to bp_core_general_settings_after_save. Within your custom function you should use wp_mail() to send the email.
—> in any file i can find bp_core_general_settings_after_save or i add it in bp-custom.php??