Okay, go to a preset folder where you have not made any of your custom presets. Then, paste all of your downloaded pres3et files inside of there. Then, go into the new preset material file, open it with NotePad. On the top left you should see File Edit Format View Help. Click Edit. A drop down box should appear, you should see Replace on the drop down box, click it. Another box should appear that says Replace on the top left corner of it. There should be a Find what: and a box where you can type something in. Type in in that box next to Find what: preset_4.
Now, below it, should be a Replace with: and a box to type in. In the box to type in, put in preset_5 (Or the preset number you put the files in, 6, 7, 8, 9, 10, 11, 1, 2, 3, 12...) Then click on Replace all. And then, click on File, Save. Now you can test that in the game. But not as Preset_4, test it as whatever preset number you chose. Got it?