pad editor

Open the PAD EDITOR, click ​one of the modes you want to re-assign -- I personally never use the 6th one; KEY SHIFT:

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So click the drop-down and change it to SP.SCRATCH:

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To activate the 6th pad mode, I would press SHIFT+BEAT LOOP on my controller. For the DDJ-1000, press SHIFT+PADFX1.

To load a sample, simply press the pad corresponding to the sample you want to load to the deck, and to unload it, press SHIFT and that pad again.