I use microsoft office rarely, I have a customer with a Microsoft Access project.
I use it once every few months to fix or add stuff.
The trial version I used expired and I found there is a small exe that will extend the trial for another 30 days.
You can use it for up to 5 times – I've been told.
the file is located at: /host/Program Files/Common Files/Microsoft Shared/OfficeSoftwareProtectionPlatform/OSPPREARM.EXE