if your referring to creating DD from a cdlc that does not have DD the only way i know which has worked for me is using the most current Rocksmith Tool kit when you open the toolkit you will see along the top tabs 1 of them is DD click that this will open the song creator where youll see large box that says path next to this box is a add or delete tab choose add then this will open a window locate your dlc folder through this open screen then select the cdlc you want to be DD once you choose the Cdlc and choose it you should be back on the song creator page the cdlc should now be listed in the path box.
then below this path box youll see options should say ddc_default i scroll down here and choose ddc_8_max_levels. then you can choose to overwrite file i would copy it to another location until you understand or make a mistake. if you dont choose over write you will have 2 cdlc's with same name 1 with DD 1 without once you do this click Generate DD this will take a minute it will take longer the more songs you do at the same time. this will create a cdlc that has DD which didnt have DD if this is what you want. hope this helps