Absolutely. While Suggested Share Text might be pre-populated for you, it's only a suggestion. You always have the option of editing, replacing, or removing the suggested share text. You can customize the suggested share text for any piece of content, and you can also set different share text for Twitter and for other channels.
Our Member Guide has an article on Sharing Posts to your Social Media Networks that will show you how to change that comment.
noteThe only text you cannot change is any disclosures that your company may be legally required to add. You will be able to see this additional text by clicking the View Appended Text link at the bottom of the share window.