An alternative answer, which I find simpler than working with inline strings, is to put TextBlock(c x:Name) inside Hyperlinkand then call its property Textin the code behind:
<TextBlock Margin="98,190,116,133.418" FontSize="14">
<Hyperlink Name="hyperlink" RequestNavigate="Hyperlink_RequestNavigate">
<TextBlock x:Name="hyperlinkText"/>
</Hyperlink>
</TextBlock>
, hyperlinkText.Text, :
private void Button_Click(object sender, RoutedEventArgs e)
{
this.hyperlinkText.Text = "some custom text";
}