Tax reform will eventually impact the Enrolled Agent Exam, but not for a while.
The IRS has informed us of the following:
For the Special Enrollment Examination (SEE), from May 1, 2018 – February 28, 2019, all references on the SEE are to be the Internal Revenue Code, Forms and Publications, as amended through December 31, 2017. Also, unless otherwise stated, all questions relate to the calendar year 2017 tax law. Questions that contain the term “current tax year” refer to the calendar year 2017. In answering questions, candidates should not take into account legislation or court decisions after December 31, 2017. In other words, tax law for the SEE is a year behind and you should expect to see no changes for the 2018 tax law until May of 2019.
That means that the Enrolled Agent Exam is not significantly impacted by changes brought about by the recent tax reform enacted by Congress. If you feel more comfortable testing under pre-reform tax rules, make every effort to test this year.
 Internal Revenue Service, Quarterly CE Provider Calls, January 9-12, 2018,