Is the repentance of my friend acceptable, given that he created pornographic pages under a pseudonym, corresponded with people impersonating a non-Muslim, and cursed veiled women, all under the pretext of his anger to defend Islam and deter its enemies, especially since he feels remorse and believes he committed major shirk? Is his repentance acceptable?

It is not permissible to use unlawful means in calling to Allah, because religion is not aided by spreading nudity, immorality, and slander. If an action leads to insulting Islam or the Prophet, then it is not permissible as a preventative measure. Your friend must repent for what he did. What you mentioned is not considered apostasy, and he must repent for what he did. He must also repent for insulting veiled women, mocking them, and he should speak well of them. Your friend's remorse is commendable, as long as it does not lead to despair.