Bitcoin Forum

Given that you think that your post (from several months ago) is a great help to the bitcointalk community and it was overthrown to the last pages because of the other posts which you think are not that useful and repetitive in nature,

can you lock your post and repost it again?

Why would you feel the need to post it again? If you chose a good topic/title, people will find it if they use the forum search or e.g. Google. The thread overview is no advertising board.
If you think that your info has value and you'd like to share it with people who need it, link to your thread in other threads that are discussing your topic.

As per rules (https://bitcointalk.org/index.php?topic=703657) - you're allowed to 'bump' your topic once every 24 hours. But I understand that rule was meant primarily for Marketplace board.

Re-posting the same content could (rightfully) earn you a ban for spamming. It's perfectly normal for topics to slide out of the first page to make room for new ones. You can always rehash old discussion, if you have anything new and valuable to add, just use 'edit' option to update first post + reply with info on the update you've made.

And if your old topic got polluted with idiotic, spammy replies and discussion became impossible to follow - you can open a new, self-moderated one - just add a short info explaining the reason for re-posting.

In my opinion, a problem always has so many aspects and arguments to discuss more and more. Therefore, what you need to do is expand and develop it in another post, not action like repost this because "it was overthrown to the last pages because of the other posts".