You can not. Once a system is activated, this activation cannot be removed because the license is stored in the Microsoft servers and not in the user's system. MS checks the hardware ID (HWID) and if a license is found in their database, the system will automatically activate.
-**Is MAS safe? How to know if there is any malware?**\
MAS is fully [open source](https://github.com/massgravel/Microsoft-Activation-Scripts). You can open the batch files with notepad and verify it. It has many users/stars on Github. You can even perform the activation manually, check Doc section for instructions.
O365 can not be activated with KMS. To activate it, the script installs Mondo 2016 licenses and activates that. This license is near to O365 feature-wise, you can get offline features of O365 but you can't get Online features of O365.
It's because it's a community project and involves many contributors, splitting donations is not practical and also because profiting from piracy is not good.