Is it possible to open in default browser a URL from command line reusing same tab?
You can do this with some AppleScript. For Google Chrome it looks like:

on run argv
  tell application "Google Chrome"
    set URL of active tab of window 1 to item 1 of argv
    activate
  end tell
end run


You'd save that as a script file (.scpt) on disk and then call it with osascript from the command line. For example, if you saved that as ~/bin/chrome.scpt you'd do:

osascript ~/bin/chrome.scpt https://apple.stackexchange.com/


to open https://apple.stackexchange.com/ in the first Chrome window's currently active tab. If you wanted to make it a little simpler you could prefix the script with #! so it can be executed directly from your shell like so:

#!/usr/bin/env osascript 
on run argv
  tell application "Google Chrome"
    set URL of active tab of window 1 to item 1 of argv
    activate
  end tell
end run


And then save that as ~/bin/chrome and chmod u+x ~/bin/chrome and call it like so:

~/bin/chrome https://apple.stackexchange.com/