A qualified disaster distribution is not considered to be a modification of the SEPP plan. From IRS Pub 590-B:
Qualified disaster distributions aren’t subject to
the 10% additional tax (or the additional 25% tax for certain
distributions from SIMPLE IRAs) on early distributions from qualified
retirement plans (including IRAs). Also, if you are receiving
substantially equal periodic payments from a qualified retirement plan,
the receipt of a qualified disaster distribution from that plan will not
be treated as a change in those substantially equal payments merely
because of the qualified disaster distribution. However, any
distributions you received in excess of the $100,000 qualified disaster
distribution limit may be subject to the additional tax on early
distributions.
Pub 590-B: https://www.irs.gov/publications/p590b#en_US_2017_publink100073843
