On a slightly related note, I'd like to also unmanage applications as well as nodes. I've tried the following URLs but to no avail:
https://host:17778/SolarWinds/InformationService/v3/Json/Invoke/Orion.APM.Application/Unmanage and https://host:17778/SolarWinds/InformationService/v3/Json/Invoke/Orion.APM/Application/Unmanage but to no avail.