Undoing mv foo.txt{,_}

[René Wilhelm <rene.wilhelm@xxxxxxxxx>]

Hello,

what would be a convenient way to remove specified trailing characters of a
string in ZLE?

For example, when I quickly want to add a suffix to a string/filename, I
usually do

mv file.txt{,_}

What's a good way to move file.txt_ back to file.txt, or more general: how
to remove the suffix of a string, without putting it in a variable first
(e.g. a=foo.txt; mv $a $a:r)?

Thanks,
René