Answer to original post at How to customize/change the text on the hosted checkout page

By using some CSS hacks, you can make every default invisible and use the ::after keyword to insert your own content as follows:

.invoiceFrequency { visibility: hidden; display: none; }
.initialInvoice { visibility: hidden; display: none; }
.taxInformation { visibility: hidden; display: none; }
.singlePlan{ visibility: hidden; display: none; }
.planSelection:after {
  font-size: 20px;
  font-weight: bold;
  color: #4E4E4E;
  content: 'Headline';
}
.contentBox:after {
  content: 'Body text describing the features of your plan.';
}