No idea about punching 100 lot order because I have never punched a single order of 100 lots in my entire trading life..........I am a very small trader/investor.
With increased margins, day trading volume( of traders trading with small margins) will go down initially but market participants will adjust to the increased margins quickly in my view.....changing market lot,charging upfront margins ,increase in margins have just a temporary effect but market adjusts with the new regulations quickly is what is my experience.