Though earth is a probationary state, "acting" is not limited to this state of life for we will still do much after death. Remember the same sociality which exists here will still after death and Alma says all things will be restored to their proper order, corruption to corruption and so forth. Which means if I will be who I am currently, in the the spirit world, then I will still be capable of sin and righteousness as spirit because we take who we are there not our bodies. Proxy is proxy because of body where it not so baptisms would be performed in spirit world. The one sin I'm sure we cant commit in spirit world in is murder since spirit in eternal so how to kill it is a tough one.