as mentioned in the post from @sdidier not possible as functionality but I want to point to additional alternative option:
One option to create some diagrams (but with some significant additional work) is to use the SVG file format. You can generate this format dynamically and it could display anything - means diagram like bar or curves etc. but also a text. For this you need to check the svg format which is part of the HTML 5 default functionality so far I know (see also https://www.w3schools.com/html/html5_svg.asp ,
Another point is how to edit for example a 3dImage which display a SVG file format containing some text.
You can use a click event to start a popup dialog where you can edit some text / on mobile device/ or on HoloLens you can create a virtual keyboard – this require some additional work and could be implemented as 3d images which displays the different characters where you can click to add an character to the dynamic svg. )