Aren't commandments intended for believers to follow?

[MineralMan]

4. Well, assuming an existing deity, it's the height of arrogance to

create additional "Commandments," I'd think. Perhaps even dangerous, should that deity be jealous of its authority.

The deity described in the Old Testament is supposed to have declared itself a "jealous god."

Exodus 20:5 King James Version (KJV)
5 Thou shalt not bow down thyself to them, nor serve them: for I the Lord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;

and

Deuteronomy 6: 14-15 King James Version (KJV)
14 Ye shall not go after other gods, of the gods of the people which are round about you;
15 (For the Lord thy God is a jealous God among you) lest the anger of the Lord thy God be kindled against thee, and destroy thee from off the face of the earth.

Were I a believer, I think I'd avoid making additional Commandments. You wouldn't want to piss off the deity, after all. Bad-tempered deities are scary!