Sorry for another "In Wordpress..." question but here we go...
In Wordpress, I can use ACF to add custom fields to a single page. This is done either in code or in the GUI by basically doing something like (pseudocode),
if id = 123 add_field "Phone Number" end
This is especially useful on homepages or landing pages where the layout is unique and I want to provide structured data entry without needing to create a custom type that is only used once. In Drupal, I dont see a way to dynamically add fields to an arbitrary piece of content. Is this possible? How?