Hi @Bryan
Thank you for your reply. 
Bokeh output is HTML + JS so in principle the DOM content of Bokeh output could be modified outside Bokeh
Yes, I can do that experimentally, but in environments where the results are displayed in an iframe, such as jupyter notebook, I can’t use the way to change it from the outside.
The Bokeh core team has recognized this as a deficiency and an important area for improvement.
I think it is a very exciting activity. I am looking forward to its further development.
On the other hand, for the following project I am working on, I would like to take some workarounds, such as giving roles to canvas, in order to proceed with the proof of concept in the near future.
Do you have any advice on which file to start looking at when considering a pull request?