What the Oral Torah Says About This
Deuteronomy 4:2 and 13:1
The Pharisees discussed the prohibitions against adding to or taking away from the laws of the Torah (Deuteronomy 4:2 and Deuteronomy 13:1). They called these prohibitions Bal Tosif and Bal Tigra.
Maimonades Law of Rebellion 2:9
Ecclesiastes Rabba 3:1
B. Megillah 14a
The point made by IsraelAlia is that these are pronouncements on the substantive law of Torah that have not followed the procedural laws of Torah.
Substantive laws about Torah can only be made by Priests and Judges.