If a rocket (flight duration 1, 2, or 3) is shift right-clicked into an enchanting table, the NBT tag is removed. This results in the pre-rocket-powered flight rocket without any flight duration tag.

This has the effect of making any flight duration 2 or 3 rockets into the old-style flight duration 1 rockets.

If you shift right click a 1, 2 and 3 flight duration rocket into the enchanting table, they will all stack afterwards so this is not merely cosmetic.