To change the priority of encoding detection on file opening:
Though you can change the order of encodings, you cannot delete them. Just move down the encodings you don't use.
Besides, “Unicode (UTF-8)” and “Unicode (UTF-8) with BOM” are always handled as a set. Because the BOM (byte order mark) will be taken into account when trying encoding data into UTF-8, there is no effect on the detection precision that the order of these two encodings are fixed.