What I do : 1. Download the DLC installer 2. Open the installer file with WinRAR 3. Extract only nativePC, nativePC_dlc, and resource Folders 4. Remember, you just need to grab those 3 Folders and delete the other things after you done 5. Replace the Folders into your RE6 directory. 6. Run the game and choose Mercenaries No Mercy 7. You can also play with L4D enemies pack now
It also fixed about the Damaged/Corrupted savedata. I figured out why was that and it because the new default_mapping from the dlc installer. Like I said at Step 4#, if you copied all the files including not just the folders. I can say the new default_mapping will replace your old one and cause Damaged/Corrupted savedata.
Now everything is done. I will be waiting for anyone who want to ask something about this.