Twitter changes behavior after submitting a research paper about it to conference. What to do?
Technology and technology based applications keep changing all the time, and frequently so.

Research methodology requires that you document these changes as they happen and annotate all references with dates. For example, you may add information that can act as a sort of disclaimer: For example: 


  N.B: As of March 30, 2017, Twitter discontinued its 140 characters
  limit for replies. At the time of submission of this paper, the 140 Characters limit was still in force.