Hi @Cristian Rus , the "Sign in with Microsoft" button is an image, correct? Referenced from the document that you posted. You could change the text but you would need to upload your own custom image. The easiest way would be to download the png image and edit it in Photoshop. Depending on where you're putting this button you could also make it using HTML and CSS.
Please let me know if you have any questions!
If this answer helped you please mark it as "Verified" so other users can reference it.
Thank you,
James