Instead of inventing another paragraph format every time you need to assign a different combination of WAI attributes, you can dedicate a small set of paragraph formats to this purpose: one for each WAI attribute. The text of each instance of such a paragraph format becomes the value of the attribute:
Probably you would not want the text of these special paragraphs to appear either in printed output or in HTML output; therefore you would assign property Delete to each such paragraph format in section [HtmlStyles], and in FrameMaker make the paragraphs conditional, so you can hide them.
If a header cell in a table reads Type of Widget and you want to provide the abbreviation Type, somewhere in that cell you would place a WAIabbr paragraph and give it content Type. You would make the WAIabbr paragraph conditional so it would not appear in print. The Delete property would exclude the paragraph (as such) from HTML output, and the HTML source would show <abbr="Type"> for the cell in question.