KISS
A very simple solution. If you have changed your mind, had a change of heart, or realized the errors of your ways, and want to change/modify your position; then simply go to your original post, quote yourself and make a new post in response to your quote. That way we will all know "historically" how the discussion has progressed. That way we won't run into the problem of: "If you go back three pages in a thread and change your post, you change the whole 'flow' of the conversation and future readers will get lost trying to figure out why a response to your post doesn't relate to it at all." If you made a post leave it alone (after it being posted for several days) so you don't screw up the recorded discussion for future readers.