Inplan Roth Rollover

Is it possible to amend a 401(k) Plan with a non-elective safe-harbor to add In-plan Roth Rollovers before the end of the year?

Notice 2006-16 lists what mid-year changes you CAN'T do do a safe harbor plan.  Roth Rollovers aren't specifically prohibited.

I agree with Bri, that one may add an in-plan Roth rollover or conversion feature in the middle of a plan year for a 401(k) safe harbor plan.

Not that I make a habit of correcting typos, but that's Notice 2016-16 in Bri's post.

Footnote 1 of Notice 2016-16 references an earlier notice that provides for only temporary relief to add an in-plan Roth rollover feature to a 401(k) safe harbor plan in the middle of the year.  It is superseded by Notice 2016-16.