Can I catch error codes when using Fabric to run() calls in a remote shell?

You can prevent aborting on non-zero exit codes by using the settings context manager and the warn_only setting:

from fabric.api import settings

with settings(warn_only=True):
    result = run('pngout old.png new.png')
    if result.return_code == 0: 
        do something
    elif result.return_code == 2: 
        do something else 
    else: #print error to user
        print result
        raise SystemExit()

Update: My answer is outdated. See comments below.