acf/prepare_field

Description
Used to modify the 
$field settings or to prevent the field from being rendered within a form.
This filter is similar to 
acf/load_field, only it is applied later in the lifecycle when the field is about to be rendered. By this time, the field’s value has also been loaded.
Changelog
Added in version 5.0.0
Parameters
apply_filters( 'acf/prepare_field', $field );
$field (array) The field array containing all settings (including value).
Modifers
This filter provides modifiers to target specific fields. The following filter names are available:
acf/prepare_field Applies to all fields.
acf/prepare_field/type={$type} Applies to all fields of a specific type.
acf/prepare_field/name={$name} Applies to all fields of a specific name.
acf/prepare_field/key={$key} Applies to all fields of a specific key.
Examples
Modifying a field
This example demonstrates how to modify a specific field’s settings before it is rendered.
functions.php
<?php
function my_acf_prepare_field( $field ) {
    // Lock-in the value "Example".
    if( $field['value'] === 'Example' ) {
        $field['readonly'] = true;
    };
    return $field;
}
// Apply to all fields.
// add_filter('acf/prepare_field', 'my_acf_prepare_field');
// Apply to select fields.
// add_filter('acf/prepare_field/type=select', 'my_acf_prepare_field');
// Apply to fields named "example_field".
add_filter('acf/prepare_field/name=example_field', 'my_acf_prepare_field');
// Apply to field with key "field_123abcf".
// add_filter('acf/prepare_field/key=field_123abcf', 'my_acf_prepare_field');
Preventing a field
This example demonstrates how to prevent a field from being rendered.
functions.php
<?php
function my_acf_prepare_field( $field ) {
    // Don't show this field once it contains a value.
    if( $field['value'] ) {
        return false;
    }
    return $field;
}
// Apply to fields named "example_field".
add_filter('acf/prepare_field/name=example_field', 'my_acf_prepare_field');