Pressing Alt + n (n = 1, 2, 3, ...) and selected image is added to the special selection n
Pressing Alt + Shift + n and the selected image is removed from the special selection n
Pressing Crtl + n and the filter is set to the special selection n. Pressing Crtl + n again goes back to the previous filter setting.
This short cuts should work in the Browser View, Editor View and Full Sreen the same way, which is actually not so for the Tags. Tagging an image is done Space in the Browser View and with Crtl+T in Full Screen. Shift+T diplays the tagged images in Browser view. But there is no short cut to return to previous filter setting...

Maybe you can think about such feature for a future release. It make workflows for selecting images for special purposes like online ordering of prints etc. very easy.
As an improvement the setting for clearing special like the tags should be kept.