Of course you can test that, the update is a minor one, 2.0.20 is mainly a bug fix release, even if you remove the new dll and use the old one it will most probably work.
I plan to just put the new SDL2.dll in the old dlls package later.
edit : done !
This release as all the others was simply made to be unpacked over an old one, replacing files. Of course if you install it in a new dir it's a little awkward if you unpack the dlls package after it, but anyway it doesn't matter, it should be compatible. I just replaced the dlls in the 92x packages, but I didn't retest any 0.92 version, it should work anyway.