arrangement, an employer may elect to amend its cafeteria plan to permit any unused amounts remaining in such flexible spending arrangement at the end of such plan year to be carried over to the 2021 plan year, pursuant to rules similar to the rules established for health flexible spending arrangements under Internal Revenue Service Notice 2013–71. (b) Retroactive application An employer shall be permitted to amend its cafeteria plan to effectuate the rule described in subsection (a), provided that such amendment— (1) is adopted before January 1, 2021