we changed all our email addresses some weeks ago. It's possible to login into Office 365 with the new email address. Only in the "belongs to" field the old address is visible. Which is not a problem for us.
When I now have a look at the remaining grace time (cscript.ex"%ProgramFiles%\Microsoft Office\Office16\ospp.vbs" /dstatus) we are still fine (more than 28 days left). But I am not sure if we only have these days left till Office stops to work or if it will automatically refresh the period.
So I tried with (cscript.exe "%ProgramFiles%\Microsoft Office\Office16\ospp.vbs" /rearm) to increase this period but after that the remaining grace period decreased to 10 days - even the message was Microsoft Office rearm successful.
How may I be sure that Office 365 really is able to refresh it's license by itself and that not all Office instances stop their work in a few weeks?