Note: This is valid CSS, but I recommend against using this trick (:before and :after psudo-classes) too widely because search engines and people using screen readers will not be able to 'read' you new text.
Use this to hide current text:
.libListReptEntAttchLble > span {
}
Use this to create new text:
.libListReptEntAttchLble:after {
content: "Click an icon to view attachment";
}