How can I customize the “DEFAULT” App Launcher in Office 365? (Is it possible?).
How do you want to customize it? What tiles are displayed? Style and color?
The app launcher is built to be customized by a user and not at the enterprise level.
https://support.office.com/en-us/article/Personalize-your-Office-36…
I would not recommend making any styling changes to the defaul tiles or structure as this has been an area that has been changing a lot recently especially around risizing and moving around. Also it is not currently possible to set what tiles are “on” by default for all employees. Administrators can add new tiles as options but a user must go pin them to their own app launcher.
The ability to manage end user tiles is very highly voted in O365 user voice.
