Does the Botox lip flip weaken the muscle and make the lip and philtrum longer over time?

When you use Botox over the long term, the treated muscle does tend to lose some strength. This translates into needing less product to create the same result. As for Botox lengthening the philtrum in a lip flip, again, this would take some time. Simultaneously, your face will be aging and your philtrum (and everything else) naturally extending/sagging. However, that effect can be remedied with fillers and staved off with treatments that make your skin stronger and firmer, such as lasers.  Please consult a board-certified dermatologist who can help you get a beautiful lip flip while preserving you current philtrum length over the long term.