Description
The node labels are currently read from the Newick string into a JSON object by Phylotree (using d3_phylotree_newick_parser), which it then renders 5A7C as an SVG representation. Editing the intermediate JSON object would modify the SVG representation, but would be overwritten by the Newick string on the next render. However, editing the Newick string directly is pretty challenging.
The best solution would be to convert the intermediate JSON format back to a Newick string every time a label is modified. Phylotrees have a phylotree.get_newick method that can do this. Since this is not immediately urgent, I've decided to file it as an issue and add this feature later.
(If you really need to edit the Newick string right now, you can do so directly in the Newick editor.)