Custom reference field settings in different content types I have a field called booked user and two types of content types, event-type-A and event-type-B. 

I am referring to the same field from both content types. However, along the process I figured out that I want to have multiple values for this field in event type-A and single value for event-type-B. Initially both had multiple values.

Whenever I change the field settings in one content type, it also changes in the other. 

How can I overcome this? Considering that I have content created in type-B and I can not really add a new field to replace that one, cause I will lose all the previous field content for that user.
The solution a colleague proposed is to add the following code in the hook_form_alter():

$language = $form['field_user']['#language'];
$form['field_user'][$language]['#multiple'] = 0;


If you want to be a bit more aggressive on data consistency you can also hook into the form validator and check that the correct number of values is inserted.