Why not just use a BR and set its "display" to "none" at the appropriate breakpoint(s)? Why abuse HR in this way?
Sure, you don't want to override it for the entire web site, but if you're being specific enough about showing/hiding line breaks at certain breakpoints, then I don't see why you can't just specify with the class of the container (or whatever) which particular BR you want to hide in a given context.
:D
<strong>Headline</strong><br> The quick brown fox jumped<hr> over the lazy dog.
And the code is clear and easy to read.