To what extent is it acceptable to use AI to enhance regular forum posts?
If English isn't your major language you should've posted in locals. I don't know why you'd consider using AI to enhance post quality. If the post gets tagged with AI detected allegations you'll be considered for ban. You don't need AI for post improvements.
AI generated post is not really your opinion and there are high chances you will not even learn anything from the conversation neither will you understand in details, what you posted.
If learning's the reason he wants to use AI for posts it won't work to benefit him.