Already possible, see the doc at https://www.e-dynamics.be/wordpress/category/documentation/7-placeholders/7-2-events/ :

#_ADDBOOKINGFORM_IF_NOT_REGISTERED adds a form which allows the visitors to register for an event. The form is displayed only if RSVP is enabled for the given event and if the user hasn’t registered yet (only possible to detect if the RSVP is for WP registered users only). See the placeholder doc concerning ‘Registration form fields’ to change the format of the form.
#_CANCELBOOKINGFORM_IF_REGISTERED adds a form which allows the visitors to remove their registration for an event. The form is displayed only if RSVP is enabled for the given event and if the user has registered already (only possible to detect if the RSVP is for WP registered users only).

Also, there are several conditional placeholders, to be used with the [eme_if] shortcode. See https://www.e-dynamics.be/wordpress/category/documentation/7-placeholders/7-1-conditional-tags/

Hi all,
Sorry to dig out this old topic, but…
Summary: even if i use #_CANCELBOOKINGFORM_IF_REGISTERED the cancel form is visible all the time.

long story:
Wordpress: 5.3.2
EME: 2.1.69

1) single event is configured like this:
#_STARTDATE – #_STARTTIME<br />#_TOWN<br />#_NOTES<br />#_MAP<br/>#_ADDBOOKINGFORM_IF_NOT_REGISTERED<br />#_CANCELBOOKINGFORM_IF_REGISTERED<br />

2) the RSVP setting in the single event dictates, that only a WP user can register for an event.
so, firstname,lastname, phone, email will queried from the WP user and pre-filled.

3) nevertheless: if i am not registered for an event, i can see both the #_ADDBOOKINGFORM_IF_NOT_REGISTERED and the #_CANCELBOOKINGFORM_IF_REGISTERED
whereas: if i am registered for an event, i can only see the #_CANCELBOOKINGFORM_IF_REGISTERED (so, this works just fine.

Did i miss a setting somewhere? is this even possible?
thanks,
Ron

here as well: thank you for this quick fix!
Works like a a charm
Ron