Probability control on enchanted books?

Enchanting books on a table is basically unpredictable, in its current state. At the moment, trading librarians for enchanted books is far easier and more useful than using an enchantment table. However, the table could be made more efficient and useful, given some alterations. In most fantasy themed games and books, creating enchanted weapons can be random, but more often it isn't. I'd propose a modification which would allow players to place an enchanted book on the table, in place of the current book, which would allow up to a 30% chance of acquiring that specific book, upon enchantment - 10% for base enchants, 20% for teir 2, and 30% for teir 3. And, it would make sense if a teir 1 copy of the book had a lower level, while increasing the enchanent level with each teir, andaxing out only at the level of the book placed on the table. So, if a player places a sharp 3 on it, they can get sharp 1, 2, or 3, but never higher. If the book is sharp 5, maybe it progresses from sharp 1, to 3, then maxes at 5 - or some variation on a scale. Alternatively, it would be interesting to see a module added to this idea, where a player could also reduce the odds of getting the enchantment on the book placed on the table. The graphic would be, maybe, an upright or upside down book, depending on the operation - increasing or decreasing odds. But, reductions on probability would be nice, to prevent overpowered or rapid enchanting, like a limit on how often a book can be used before breaking.