When you change the source hierarchy all data gathering with the original hierarchy is stopped and all shared distribution ...

When you change the source hierarchy all data gathering with the original hierarchy is stopped and all shared distribution points between the original source hierarchy and the destination hierarchy are removed. 

If you have distribution point upgrade job that are not complete  and you specify a new hierarchy , this can result in distribution points that do not function correctly. Make sure that all your distribution point upgrade jobs are complete before you continue.

Do you want to change the source hierarchy now?