In the "material" dialog box
1- Create a new library with the name (00_ my materials) , for example.
2- go to the old folder of "ddc Most_Freq_Used materials"
3- go to the interior folders
4- right button copy >>> go to the new folder >>> right button paste
You will have your new folder at the top.
Do test first.
I think undercore (_) might also work but I never tried - obviously, the letter is not working