Is there a way to set the value of the user.maui.retentionStart attribute via the REST API?

Hello,

I have determined by experimentation that I can update the user.maui.retentionEnd and user.maui.retentionEnable attributes on an existing object via the REST API as long as that object is currently associated with a policy that specifies retention, however any attempt to update the user.maui.retentionStart metadata attribute on the same object fails. Is this because it is not possible to do so, or is it because the Policy is not configured with a Start Delay Window?

Thanks,

-Eric