This is in the context of mythology, where the subject or the creation of a god tries to overthrow, challenge or directly assails the god.
Perhaps you could use some expression like "insurrection against the heavenly throne". But if there was a single word for it, some author would surely have used it already to describe Lucifer's rebellion.
"Deicide" could apply to the outcome of a successful attempt, and by analogy with regicide we might seek a "regi-" word that applies to an attempt to overthrow a king. If one existed, we could apply "dei-" to it. But I don't think there is one.
There are words like "mutiny", "rebellion", "revolt", "uprising" and so forth, but these apply to an action against any dictator or feudal overlord. There is no evident way to append a prefix to these to make them apply specifically to a king. And if we can't coin a single word for the far more common case involving a king, then it is hard to imagine that such a word exists for the much more specialized case involving a god.
Edit: by analogy with lèse majesté, you might coin a phrase like lèse divinité or lèse déité.
If the subject is rebelling against his religious beliefs (e.g. his god's directives), then you could use the word heresy. In other words, the subject is a heretic. However, I just noticed you already rejected apostasy because you want to focus on a physical attack.
In Greek mythology, the Titans were a race of giants who fought with the Olympian gods. In that spirit, you could say your subject fought a "titanic battle" against a god, though the average reader wouldn't understand the significance of the word titanic.
Other words that come to mind include hubris (the perhaps foolish idea that one could beat a god) and heroism. You're describing a David and Goliath struggle but on a much higher level.
(Law) the crime committed if a person insults, offends, or vilifies the deity, Christ, or the Christian religion.
: open or bold resistance to or disregard for authority, opposition, or power.
A huge and powerful warrior-king who virtually embodies defiance against his highest god, Capaneus is an exemplary blasphemer--with blasphemy understood as direct violence against God. Still, it is striking that Dante selects a pagan character to represent one of the few specifically religious sins punished in hell.
I found a word that works well for the particular context in my writing: Treason
- the offense of acting to overthrow one's government or to harm or kill its sovereign.
- a violation of allegiance to one's sovereign or to one's state.
- the betrayal of a trust or confidence; breach of faith; treachery.
Although there is nothing explicitly god-related in this, the things regarding "sovereign" seems appropriate for offense against a god. Beside, the word "treason" almost always have negative connotation, which would be appropriate when the action is described by those who believe in the god.