Yes, the option to change a registered category is guaranteed until at least 30 days prior to the date of the event, it is the organizer’s choice to determine how many further days of category change are permissible (right up to zero, being the last day of registration) once the 30 day period has been reached. This is set at event creation and can be increased but not decreased.
The default setting is 0 days prior to the close of registration meaning that a registrant may change their category (subject to space in the new chosen category / event) up until the published close of registration or until the event sells out, whichever is sooner.