Half an year ago, I wrote about the possibility to edit the default policy in SfB Online here. Then Ignite happened, and among the myriad of other good news, we saw for the first time the ability to create custom SfB policies in Office 365.
Now, this functionality has been rolled to all Office 365 tenants, giving us greater customizability and further closing the gap with On-Prem SfB installs. Read more about it here: http://blog.enowsoftware.com/solutions-engine/using-custom-policies-with-skype-for-business-online