When you right click on material and the list pops up you can select Manage Favorites. If you do not want what is in the list you can select it then select Remove. If you want to add to the list just find the material you want in the left of the window then select add to add it to the favorites list that way it will always be there when you right click on material.
You can also open up the material file (.sldmat) in notepad and
add materials as needed. Understadn if you do it this way it is written in code.
Not hard to figure out once you examine it.