Thanks.
in WinXL, F3 invokes the Insert/Name/Paste dialog. Using the menu
command works on the Mac, too.
You can even assign a keyboard shortcut to it (Tools/Customize/Customize
Keyboard..., and choose the Paste... item from the Insert category).
However, in MacXL, using a keyboard shortcut usually takes you out of
edit mode, so you'll either get an error (if the existing formula isn't
syntactically correct), or the name will overwrite the formula.
I haven't found a workaround for it, though I have in the past created a
userform that allows editing the formula and inserting a name. It was
useful for one client, but to me seems more trouble than its worth...