pmpro_cancel_previous_subscriptions

This hook controls whether or not PMPro cancels a user’s previous membership level at checkout, which is enabled at default. This is dangerous, but is useful in certain cases like the PMPro Addon Packages plugin.

pmpro_check_discount_code_levels

This filter controls whether discount codes should only be applied to certain levels. By default, this is set to true, and discount codes are checked to see if they apply to the membership level passed. Return true if the code can be used with the level supplied or false if not.

pmpro_field_classes

Use this to filter the CSS classes added to the fields on the checkout page. This is normally used to handle error highlighting with the “pmpro_error” class.
This returns the CSS classes and the current the current field name to be applied to.

pmpro_member_startdate

Filters the pmpro_getMemberStartdate function. Passes the $user_id, and the $level_id as parameters.

pmpro_after_change_membership_level

Use this hook to execute custom code after a user’s membership level is changed or cancelled. This hook passes the new level ID, the user ID of the WordPress user, and the level ID being cancelled (if specified).