Take and copy a screenshot on Mac

Rather than risk potential future calamity by reassigning keyboard shortcuts away from pre-configured operating system settings, why not take advantage of the Automator action Take Screenshot, where you can tell it that its type is interactive, that it is to allow you to choose a selection, and Save it to the clipboard. Saved as a Quick Action, you can launch it with a unique keyboard shortcut (e.g. ^x), and you can verify what was sent to the clipboard via Finder : Edit menu : Show Clipboard.

1. Launch Automator > New Document > Quick Action > Choose.
2. Drag Library > Utllities > Take ScreenShot onto the larger workflow window
   1. Workflow receives [ no input ] in [ any application ]
   2. Change nothing else in that header
   3. Take Screenshot
      1. Type: Interactive
      2. Options: Choose Selection
      3. Save To: Clipboard
3. Save (named mine: Capture to Clipboard
4. System Preferences > Keyboard > Shortcuts > Services (look for the name you gave it)
   1. Click "none" text, and it changes to [ Add Shortcut ]
   2. Click [ Add Shortcut ] and enter control key and x, followed by a return to set it.
5. Now, anywhere you click ^x, you will be prompted to click on the screen, and the familiar selection cross-hairs will appear. As usual, when you release your selection, the capture is put on the clipboard.

Just try the contol-x keystroke as I did in my example. It worked immediately. My service, which I named Capture to Clipboard works just fine using that shortcut. With Mojave, you may have to click on Safari (by example) and choose the Capture to Clipboard service from Safari menu > Services sub-menu. Once should be enough, and then afterward, the keyboard shortcut should work.

There have been considerable updates to Mojave after 10.14.4, that you might consider applying, as that currency will determine whether you receive future security and browser updates, or not.

Shift-Command-4 for screenshots (Take a screenshot on your Mac - Apple Support)

Please see: Mac keyboard shortcuts - Apple Support

Hope it helps.

FWIW, I believe the user is talking about copying a screen shot directly to the clipboard.

Ok. Sorry, misunderstood.

I'm not sure if we can modify the key-shortcut. I did check in keyboard shortcuts, only toggle enable/disable is available.

It's always possible. For example in Firefox cmd+4 switches to the last open tab. You'll just have to see.