the general idea is to have a topic to post every week and leave a message to our loved ones of the future, as you know, our posts are hosted on the #hive blockchain, and everything that is published after seven days cannot be modified or altered, and the message will be there forever

Not only after seven days.

Content published on the Hive blockchain cannot be edited, modified, deleted from the blockchain at all.

Even if you edit/modify, or delete a post/comment, you edit/modify, or delete it only on/from the frontends.

But it can still be visible on the blockchain level.

Every post/comment edit/modification is visible on the blockchain level.