Enable the cell field plugin for both column headers and first-row cells, instead of restricting them to text inputs only

The headers and the first column all use plain textfields. I have a use case where I would like to have some of the text in one of those fields use italics.

Example of what I am trying to accomplish (and how it's not working):

However, this is not allowed in a plain textfield, and I have been unable to discover any way of overriding either the settings for those cells. I have also been unable to override the template for table.html.twig with any sort of specificity as there is nothing in the $variables that are sent to the preprocess or theme suggestion hooks to identify tables generated by this module versus other tables, or to identify this specific table versus other tables.

Any suggestions?