Customized meter messages

I'm trying to customize the message below to include a promotional offer of 99 cents for a month. I've tried putting in metered_sub_final_message in the URL custom properties but it won't change the text. This is what I'm trying to add:

<a style="font:bold 13px Arial,sans-serif; color:#21491d; padding:10px 10px; background: repeat-x scroll 50% 50% #d3e0cd; border-radius:4px;" href="https://thebrunswicknews-dot-com.bloxcms.com/users/admin/service/purchase/?serviceid=3767&driver=subscription&referer_url=/users/admin/service/purchase/&step=1">99&cent; Trial</a>