QACA auto enrollment % change January 1

A current QACA safe harbor plan auto enrolls at 3% and escalates to 6%. Effective 1.1.2019 (calendar year plan) sponsor wants to amend the document to auto enroll new participants at 6% and increase to 10%. 

Is there a restriction on sweeping back and bringing all participants without a positive election to 6%? For participants who have already been escalated to 6%, is there a restriction that would not allow us to annually increase them to 10%? Will we end up with two different groups of QACA participants?

I have reviewed the plan document and there does not seem to be any mention of what happens when the default rate changes. Also reviewed the EOB and don't see anything there either.

Thank you