Symptoms
After an Office 365 update, editing application instance settings is not possible, the error is faced:
'base_domain': can't update property marked as 'readonly'
or
'packageRelease': can't update property marked as 'readonly'
Cause
The instance settings have not been refreshed in IIS cache.
Resolution
Login to the Office 365 Endpoint server and restart IIS services:
iisreset