Filter the new level for the user as passed in to the pmpro_changeMembershipLevel function before it is added to the member.

apply_filters( 'pmpro_change_level', $level, $user_id, $old_level_status, $cancel_level );

Parameters

$level

int ID of level to set as new level. 0 if the user’s membership is being cancelled.

$user_id

int ID of the user to change levels for

$old_level_status

string The status to set for the row in the memberships users table. (e.g. inactive, cancelled, admin_cancelled, expired) Defaults to ‘inactive’.

$cancel_level

int If set, cancel just this one level instead of all active levels (to support Multiple Memberships per User)

Source

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/includes/functions.php