The relevant issue here basically boils down to whether others have found your content valuable. From a quick look at your profile, that appears to be the case.
Note that significantly changing the content of a post after the fact can be seen as defacing the content, which in severe cases can actually get your account suspended for vandalism, even if it is your own posts. This is especially true if people have spent time answering a question, or if there have been upvotes on the post, but other factors can also be at play there. So you certainly can flag a post and request deletion, but it is highly likely that such a flag would be denied. As Monica Cellio stated, moderators generally won't delete posts that the post owner can't delete normally (and even if deleted, they will still be visible to high-reputation users).
Keep in mind the terms of service, specifically section 3 "Subscriber Content", which starts out by stating (my emphasis):
You agree that all Subscriber Content that You contribute to the Network is perpetually and irrevocably licensed to Stack Exchange under the Creative Commons Attribution Share Alike license. You grant Stack Exchange the perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works and store such Subscriber Content and to allow others to do so in any medium now known or hereinafter developed (“Content License”) in order to provide the Services, even if such Subscriber Content has been contributed and subsequently removed by You.
Additionally, the entire purpose of this site is to be findable. The entire purpose of the whole Stack Exchange network is to increase the corpus of knowledge on the Internet.
So, unfortunately, there isn't a lot you can do. If you aren't willing to perpetually license what you post to Stack Exchange, then you shouldn't be posting it on any site in the network. If you don't want the people you are involved with to find your posts here by searching, and possibly derive plot points and spoilers from them, then you will simply have to fudge what you do with them enough that it isn't readily recognizable as being based on the questions you have posted and answers you have received in return.