Customizing text on x unified hovering

Arg. I have now had this come up again in another context. This time I have an x-unified hovermode for a line chart with multiple categories. Example:
tmp10

In this case, I want to do two things: 1) remove the x-axis title label (‘2022’); 2) add a line of text once to the bottom of the hover (below Grade 6) with some information that is stored in another column of the dataframe used to make the chart. I know that I can use custom_data and hovertemplate to add the extra information, but this ends up adding the information to each trace, which is not what I want. What I want looks something like this (although with better spacing):
tmp11

Sample MRE code (not for this exact chart, but a chart that can be used to illustrate the problem) is available in my earlier April 24 post.

I’m guessing at this point that this is not currently doable? Would it be hard to fix?

Thanks,
eb