In order for the plan to be changed from a regular plan to a plan in which you can make an early withdrawal without penalties from the assistance holdback amount, the beneficiary must file with their financial institution an election and a medical certificate from a medical doctor. That would then be filed with the Canada Revenue Agency and Human Resources and Skills Development Canada, and they would keep it in their records that these amounts may be withdrawn without penalty.
In order to reverse that election, the individual merely needs to file a notice that essentially says they wish to reverse that election.