FAQ Q380: Can some reservation form items be hidden on the reservation form and filled out by the customer at a later time?

Yes, you can do this by adding form items of type hidden (only for special usage). These fields by default will only be shown to the administrators and never to the customer. Note that you can still use the field Comma-separated values with this item type if you'd like the hidden field to be a dropdown with pre-defined values.

Your reservation process will likely involve configuring an automated email notification where you'll send to the customer a link to a page showing these special form items. Typically this would be triggered by an event such as confirmation or manual/automatic color change (see Q223), or perhaps a certain time after the reservation was made or a certain time before arrival. You may also use Planyo's messaging system (see Q349) to send a custom message to the customer which would include this link.

In order to send the link to the customer allowing them to set the hidden form items, use the tag $(complete_reservation_data_url:...). After the colon you need to specify comma-separated names of the fields you wish to display, for example if you have fields named "Hidden field 1, Hidden field 2", use the tag $(complete_reservation_data_url:Hidden field 1,Hidden field 2) -- you may also use underscores instead of spaces and all-lowercase letters.

Filling out the form by the customer will trigger the notification Reservation modified by client so you can in turn inform the administrators that the customer submitted the form. You could also add a color manager rule which would assign a new color to a reservation where a specific field has been filled out. You'd then need to set Advanced template code in your color manager event to something like:
$(if) $(prop_Hidden_field_1) $(then) true $(endif)
so that the color is changed only if field Hidden field 1 has been filled out.