How to customize Admin Dashboard home page

Hello,
On admin dashboard home page, there is an Option which allows me to customize the boxes showed on the home page. But is it possible to allow me to add some links or text myself?
For example, I may
- add a onboarding introduction created by me for new users when they first time login to their sites
- share some news/special offers to my sub-sties owners

Thanks for your help!
Regards
YZ