var replacements = new Dictionary<string, string>
{
    { "&euro;", "€" },
    { "&sect;", "§" },
    { "&nbsp;", " " },
    { "&gt;", ">" },
    { "&lt;", "<" },
    { "&amp;", "&" },
};


var messageWithReplacedValues = replacements.Aggregate(/* the string */, (current, replacement) => current.Replace(replacement.Key, replacement.Value));