You can replace the motors without removing the plastic gears (sorry you had to read this after the fact). The outer motor mounting screws can be removed readily. The inner motor mounting screws are trapped by the gears - But you do not have to remove them.... Unscrew them from the motor by picking up the motor as you loosen the screws. Position the new motor over a trapped screw and carefully tighten the screw (avoid cross-threading).

Since you now have the rotor shafts out of your bird, you may find it useful to smooth the screw marks on the outer shaft with crocus cloth before you reassemble things. The newly smoothed shaft will make it easier to reassemble things without excessive use of force.

Cannot comment on tail booms. Bought a carbon tail boom, but never mounted it after reading the stock tail seemed to give better aerodynamics.