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.message p a[href$="user_ID"]:after {content: 'Your Message';color:#8997A1;}

Replace user_ID with your friends User ID and "Your Message" with what you want appended after there name.

This only works in CSS 2 compliant browsers. Sorry no IE until the next version.

OR

.message p a[href$="user_ID"]:after {content: 'Your Message';color:#8997A1;}

appends a title only when they hover over their name.

Working example in my profile.

It is a paragraph tag.

And the a is an anchor (link).