Welcome! From my experience your question raises several other questions that should be addressed at the same time. Further information would be very helpful to provide specific help.
First, your location is important in order to understand what the climate is like in the month of december where you live.
Second, pictures of the tree would allow participants to gauge the overall risk involved on the basis of tree health, lower branches and foliage present.
Third, current condition of roots, recent work done.
Generally It is not normally reccomended to trunk chop and repot a conifer at the same time regardless of the climate.
Successfully reducing trunks and developing additional lower branches on conifers is normally a much slower process involving a longer period of time and application of techniques in preparation. Some of these steps include progressive repotting, improving the overall health of the tree, balancing growth on lower branches and staging the trunk removal to lessen the shock to the tree. The process could involve several years before the tree is cut down to the desired level.
Hope these comments help!