On that first example, "prepone" might not officially be a word, yet, but I encourage them to keep at it. Its construction follows the same structure as its intended antonym, even back to the etymology of "postpone". Unlike some of my English teachers in elementary school, the lexicographers at Oxford are not a bunch of solely prescriptivist assholes. Get the word into common enough usage that there are multiple sources for the editors of the OED to cite, and you just might get "prepone" added to the next edition. The story about an argument with Tolkien over the correct spelling of the plural of "dwarf" notwithstanding, I think included-in-the-Oxford is a standard few can argue with for an English word being officially real.