The league's appeals officer, Ted Cottrell, reduced the fine because he said Harrison understands the player safety rules and has made an effort to adjust his technique to play within those rules. NFL commissioner Roger Goodell supported the reduction.
Harrison's four fines this season for dangerous hits now total $100,000.
Harrison's agent, Bill Parise, also plans to appeal a $25,000 fine Harrison was assessed for a hit on Bills quarterback Ryan Fitzpatrick on Nov. 28.
Harrison sidelined both Massaquoi and returner-wide receiver Josh Cribbs with hits that caused concussions. He was not fined for the Cribbs hit. The teams meet again Sunday in Cleveland.
Robinson's fine was reduced from $50,000 to $25,000 and Meriweather's fine from $50,000 to $40,000.
The league announced several new fines Friday, including one on Tennessee right tackle David Stewart, who was hit for $20,000 for unnecessary roughness after hitting a Kansas City player "late and away from the play on two separate instances" on Sunday.
Indianapolis' Gary Brackett was fined $15,000 for roughing the passer, when he hit Oakland quarterback Jason Campbell in the head and neck area. Brackett was fined $10,000 earlier this season for a similar hit on Philadelphia's Michael Vick.
Oakland's Lamarr Houston was fined $12,500 for poking his finger in a Colts player's facemask near the eye.
New England's Jerod Mayo has to pay $10,000 for unnecessarily striking a defenseless Buffalo receiver in the head and neck area on a pass play. It was unclear if the fine was for a hard hit on Steve Johnson or David Nelson, both in the second quarter.
Information from The Associated Press contributed to this report.