That's a good point about previewing. So instead of "cgn", it looks like you can do "gns", which highlights the match, then enters into substitution mode, and y

That's a good point about previewing. So instead of "cgn", it looks like you can do "gns", which highlights the match, then enters into substitution mode, and you type the replacement, then hit <ESC>. Then you can hit "n." "n." "n." repeatedly, where the "n" goes to the next match so that you can preview, and the "." applies the replacement. Not quite as efficient as a single ".", but the "n." sequence is a familiar one.