Change URL multisite
https://wordpress.org/support/topic/swapping-a-main-site-to-be-a-subsite-and-a-m...
09 sep 2015 - https://wordpress.org/support/topic/swapping-a-main-site-to-be-a-subsite-and-a-main-site-to-be-a-sub-site
09 sep 2015 - https://wordpress.org/support/topic/swapping-a-main-site-to-be-a-subsite-and-a-main-site-to-be-a-sub-site