Does this negative COVID-19 test requirement amend the previous Presidential Proclamations about non-U.S. citizens entering the United States?

No; the negative test requirement does not change any of the previous Proclamations that limited entry of non-U.S. passport holders who were physically present within specific countries during the 14-day period preceding their entry or attempted entry into the United States. 

Is there the possibility that another suspension of on-campus activities can happen and if so, what should I expect?

In the event that on campus activities are suspended due to public health or other considerations, the University will provide clear guidance about how students can complete the semester remotely considering the implications from current and/or forthcoming SEVP guidelines.