GW Rest API and preferredEmailAddress on groups

Good morning,
My customer is asking:
If there is a way to programmatically change the preferredEmailAddress on groups, well any type of GroupWise object, but especially groups?
Based on the documentation, the Rest APIs do not seem to support it, but I tried it anyway, and the return message seems to confirm it.
curl -k --user boxxxxxxx-H "accept:application/json" -X POST https://boxxxxx.box.xxx:9710/gwadmin-service/domains/BOxxxxx/postoffices/GROUPS/groups/ndxxxxxxxxtestgroupemailchange --data '{"preferredEmailAddress":"something.groups.boxxxxx@bxx.xxc}'
Enter host password for user 'boxxxxxx':
{"httpStatusCode":405,"error":true,"httpStatus":"METHOD_NOT_ALLOWED"}
We have a lot of preferredEmailAddress that include the PO and domain, something.PO.Domain@bxx.cxx instead of something@bxx.cxx I would like to be able to script setting the override.
This is not a request to do anything except find out if it is possible to update this outside of GWAC.
Thank you for any assistance that can be offered to my customer. 
-Daniel