PS:
This effect can also be achieved, with a little more variety, by choosing Text Underline from the font panel. To implement this, "show effects" must be active, as shown from the cogwheel box at the bottom right of the panel.
The options are then to set a single or double underline, and also to set a colour for it, which may be different from that of the text.
To have this apply continuously (i.e., through separate words) the Option-Space means of separating them must still be used. Accessing this function has a slightly different effect, even for the single line, than the underline produced by Format / Font / Underline, or Apple / u.
Curiously enough, both ordinary and non-breaking spaces behave the same in respect of the strike-through function, which is also available from the font box. One of Apple's little mysteries!
But I shouldn't think it's a burning isssue, even for lawyers and editors. As far as I can see, you'd have to get around it by switching that option off for every space you wanted to be free of strikethrough. Assigning a shortcut might be tricky, since it's not a main menu item.
The easiest way to manage this, if it's ever needed, would be I think to assign both strikethrough on and strikethrough off to character styles in the styles drawer, which would enable toggling between them with that open.
Regards.