You sure can. Here's the steps. For the purpose this example, we'll assume you want the helper text inside the reference number field to say "Account Number". 

  1. Log into your Web site's administration (www.yourdomain.com/administrator)
  2. Navigate to Extensions > Language Manager
  3. Click Overrides (left-side menu)
  4. Click the green New button at the top
  5. Using the search tool on the right, enter the following:
  • Search box: PLACEHOLDER_REFERENCE_NUMBER
  • Search for: Constant
  1. Click the matching result from the list (if you get more than one, it won't matter which on you click as long as they are both labeled PLACEHOLDER_REFERENCE_NUMBER).
  2. Change Text (in the left column) to Account Number
  3. Click Save & Close.

If you have the cache enabled for your site content, you'll need to clear the cache before the change takes effect on your site. Once you do, you should see the altered text in the second field.