jericomovie said:agnosticism: god cannot be known
amoralism: morality is not plausible
acosmism: disbelief in existence of eternal universe distinct from God
adevism: denial of gods of mythology and legend
anarchism: doctrine that all governments should be abolished
adiaphorism: the opinion that certain doctrines or practices in morals or religion are of no consequence
Agnosticism - the truth value of certain claims is unknown or unknowable.
Amoralism - the absence of moral beliefs (immoralism is the rejection of moral codes)
Acosmism - correct! remember that disbelief means not believing.
Adevism - also correct, in this case the a- prefix does mean an explicit rejection. That's one.
Anarchism - kind of. Anarchos means without rulers, so half a point for this one.
Adiaphorism - actions not specifically prohibited may be treated with indifference.
So you provided six examples and I score you 1.5/6 in demonstrating that the a- prefix is always an explicit denial of the position/belief. It seems to me that a- can mean either an implicit non-belief or an explicit denial. When we look at the usage of the word atheism we see an almost universal acceptance of the non-belief usage. The only people confused about this seem to be theists.
I see I was beaten to the punch by australopithecus, for his interest the word diaphoros means difference so adiaphorism would be without difference (or with indifference) by his scheme.