You can find the letter here and a response from Sen. Leahy here.
The main point of the letter is to retract Schlozman’s statements that he was “directed” by Public Integrity section to file the indictments, and to say now that he only “consulted” with that section, making the indictment decision himself. But equally important is this explanation, which is sure to be torn apart by former DOJ attorneys:

My written testimony explicitly stated that the Department’s informal policy of not interviewing voters during the pre-election period, which is intended to avoid actions that could conceivably have a chilling effect on voting, does not forbid the filing of charges around the time of the election. While the ACORN matter arose in October, Department policy, as confirmed by the Elections Crime Branch (the director of which authored the Department’s election crimes manual) did not require a delay of this investigation and the subsequent indictments because they pertained to voter registration fraud (which examined conduct during voter registration), not fraud during an ongoing or contested election. Consequently, the Department’s policy was not implicated in this manner.

(my emphasis)
So Schlozman is saying that department policy did not forbid bringing the indictments, and because the indicatments related to registration fraud, they were unlikely to chill voters from voting. Even if that’s true (I’m not so sure it is on the chilling point), it misses the central issue. Missouri was involved in a hotly contested Senate race, and it is a place where vote fraud charges had been raised repeatedly by Republicans against Democrats. Bringing indictments against registrants who worked for ACORN, a group that registers poor and minority voters, was likely to (and in fact did) feed into Republican charges of Democratic voter fraud, which was likely to increase turnout among Republicans and turn independent voters away from Democrats and toward Republicans.
In one of the least believable parts of Schlozman’s testimony last week, he stated he did not believe the indictments could affect the outcome of the Missouri election (and professed ignorance on ACORN’s political leanings). This letter continues to perpetuate the idea that Schlozman had no idea the indictments he brought could affect the outcome of the election.