What would be the quickest way of yanking one word and
replacing another word with it? Something that doesn't involve
specifying registers, because that would require too many
keystrokes and I might as well use cw and type the word myself
then.
You don't mention whether you only want to do this once, or if
you have a whole bunch to perform.
If you just need to do it once, you can use
vwp
or
viwp
on your target word, and it should replace it with whatever was
in your scrap register (that you yanked previously). It has the
unfortunate (well, it could be fortunate in certain
circumstances, but this isn't one of them) side effect of then
replacing your scrap register's contents with the word that was
just replaced, meaning you can't repeat the process elsewhere,
and still get the same results (with the original contents of the
scrap register).
One solution might be something like
nnoremap <f4> "_ciw<c-r>"<esc>
which will replace the word currently under the cursor with the
contents of the scrap register, and not tromp over it with the
contents of the replaced word. It makes use of the black-hole
register:
:help quote_
Hope this gives you some stuff to work with...
-tim