The IRS has released Notice 2016-16 providing some guidance on mid-year changes to a Safe Harbor plan.

Document Excerpt
This notice provides guidance on mid-year changes to a Safe Harbor Plan under §§ 401(k) and 401(m) of the Internal Revenue Code. The notice provides that a mid-year change either to a safe harbor plan or to a plan’s safe harbor notice does not violate the safe harbor rules merely because it is a mid-year change, provided that applicable notice and election opportunity conditions are satisfied and the mid-year change is not a prohibited mid-year change, as described in the notice. In addition, the notice requests comments on additional guidance that may be needed, in particular with respect to mid-year changes to safe harbor plans in cases in which a plan sponsor is involved in a merger or acquisition.
II.

Link
https://www.irs.gov/pub/irs-drop/n-16-16.pdf