Because I found a design for a ~80% efficient 3D printable motor, but I would like to use it as a generator from a wind turbine as well.
Yes you can, and this is in fact a commonly done hack. A favorite motor to use for a generator is a permanent-magnet DC motor as salvaged from paper shredders and treadmill-style exercise machines.
Making a generator efficient requires several things: first, minimizing magnetic flux leakage by artful design of the iron parts that guide the flux to where it's needed, and then containing it within the gap between the field and the rotating armature, and second by selecting the armature wire gauge, winding number and desired operating speed to minimize heating losses in the wire. This is a solved problem in motor/generator design.
Building wind turbines means that the blades need to match the generator, as power out keeps the blades from overspeeding unless you go for a offset axis machine that rotates itself out of the wind when the wind speed is too high.
This means you need to know the range of wind speeds that you face in your location, maximum and also the common speeds that will be the bulk of the generation.
One link, among many that you will find once you start to search is:
Met him and seen what he does....