Add Energy Saver to menu bar? On my iMac, I tend to adjust the Turn off display after: from short to long and back again, pretty frequently. It would be convenient if I could get to this with one click, perhaps from the menu bar. Is there a way to accomplish this?

It's not one of the things in /System/Library/CoreServices/Menu Extras.
Native option

You're most likely aware of this, but for the benefit of others I thought it worth mentioning even though it's not exactly what you're after anyway.

By going to Apple > System Preferences > Energy Saver users will have a checkbox at bottom left of the window that they can tick to enable access via the menu bar. The option provided here differs depending on whether you have a MacBook model of some sort or a desktop computer, and also depending on the version of macOS you're running. In summary:


MacBooks will have a Show battery status in menu bar option
Desktop Macs may have no option at all, or they may have an option for Show UPS status in the menu bar (this depends on the version of macOS you're running and whether you have a compatible UPS connected)


Enabling one of the above options doesn't give the one click solution you're after, but will give you quicker access to the Energy Saver preference pane, effectively making it a two click solution instead of the usual three clicks.

3rd party options

Since there's no perfect native option I think you're best bet is to use a 3rd party menu bar utility that allows you to override your Mac's sleep settings whenever you need. 

There are numerous options (both free and paid) and ones available on the Mac App Store or not. The option you go for depends somewhat on the version of macOS you're running and personal preference.

To start with, open the Mac App Store app and conduct a search for "caffeine". This will return a number of options you can choose from. One notable option that doesn't appear on the list of search results is Amphetamine (so I link to it here separately - last time I checked it was free).

Another option not available on the Mac App Store is KeepingYouAwake. This is basically a wrapper around Apple's native “Caffeinate” Terminal command which can be used to alter your Mac’s sleep behavior. Caffeinate is Apple’s official command line utility - if you haven't heard of it and are comfortable using Terminal, then you can view more information by launching Terminal and running the man caffeinate command. Otherwise, KeepingYouAwake is a GUI version that runs it for you without having to use Terminal. Just keep in mind that the version you run will depend on the version of macOS you're using.

In summary, I'd probably start with the Mac App Store search and go from there. 

NOTE: I am not affiliated with any of the products mentioned in this answer.