Since consensus was to keep, and I still felt strongly that the lack of web accessibility was a problem, I added spans into the List of R-phrases, then converted the R-phrase template to include a #link into the list, only to discover that the link target shadows the title attribute for tooltip purposes. To resolve this, I created redirects into the list with verbose titles like R1: Explosive when dry. Template:R-phrase now links to the list via these redirects, and the redirect titles come up on the tooltip. That way, you get your tooltip, and I get web-accessibility. I hope this makes sense to you.
If ever you chem guys get around to creating separate articles on each R-phrase (and I think you could, with expanded information on the nature of the hazard, standards for storage, transport and use, and a list of chemicals to which the R-phrase applies), then you can either overwrite the redirect with the article, or retarget the redirect at the article. Either way, you won't have to touch the templates.
Hesperian