[Update: The Entertainment Software Association has acknowledged that the DMCA takedown claims against Dying Light mods were also a mistake, saying that they were improperly issued by a third-party vendor on its behalf. ""ESA was notified this morning that potentially erroneous DMCA notices had been transmitted by one of its vendors," the ESA told Ars Technica. "Upon further review, it was determined that the notices should not have been sent and retractions were issued immediately. We regret any inconvenience and have taken steps to avoid similar situations in the future."]
The Dying Light 1.2.1 patch released on Friday made various changes to the game, including to its data files in order to prevent cheating in online play. Unfortunately it quickly became apparent that those changes also prevented user-made mods from working properly. More fortunately, Techland says that was not actually its intent, and it's got a new patch in the works that will straighten things out.
"With the recent patch (1.2.1) on Steam we blocked cheating to make sure the game’s PvP system (Be The Zombie) would not be abused. This, however, had the side-effect of hindering mod-makers from making changes to the game," Techland wrote today on the Dying Light Steam page. "Creating obstacles for modders has never been our intention, and we are sorry for the inconvenience. We are now working on a quick patch that will re-enable common tweaks while stopping cheating in the game’s multiplayer mode."
"At Techland, we have always supported the mod community, and loved seeing how our own game can be changed by the players. A big part of the original Dead Island’s success was the passion and creativity of mod-makers from our community. We want the same for Dying Light," it continued. "For quite some time, we have been working, and still are, on giving modders all the power we can. We will keep you updated!"
As for complaints about DMCA takedown notices, documented in this Reddit thread, that have also impacted the creation and distribution of mods, a Techland rep said it's not entirely clear why they were issued, or even who issued them, and that the developer is looking into the matter separately.