I think you misunderstood it a bit.
go.set works fine with collision objects. It does however mess with the continuous collision detection (a.k.a “bullet”). For CCD to work, it needs to do continuous calculations, and that won’t work if you suddenly teleport the object to another place.
As mentioned to you before, to make use of CCD, you need to only use forces to act upon the object.
To help with your scenario though, there are (as mentioned) raycasts, and also shape casts. We haven’t implemented the shape cast yet, but we should put it on the short list for the next update of our Box2d Lua module.