If you have advanced developer skills, you can use a plugin to add additional functionality to BD in a way that will not be overwritten when the plugin updates.
This article provides instructions for how to add a phone number to the contact form as an example. Obviously, the code would be different for what you might want to do, and the title of the plugin can be anything that makes sense to you.
To accomplish this with BD 5.x, you need to do the following:
1) Install Pluginception from the WP.org repository. Go to Plugins->Add New. Enter “Pluginception” in the search field, hit Enter. A plugin written by “Otto” should appear.
2) Install and activate this plugin
3) From the WP Admin area, go to the Plugins menu and click on “Create New Plugin”. We’re going to create a plugin with a PHP file that you can put in the custom code. This way, your changes will never be lost.
4) After that, you’ll be on a screen with a lot of fields. You only need to fill out the FIRST one:
Call the plugin “BD Custom Contact Form Code”
Then save your file at the bottom:
5) You should be redirected to the Plugin Editor where you can edit the code of the plugin.
If you are not redirected, from the Plugins menu again, click “Plugin Editor”. Then, on the right hand side of the screen, find this control and open the drop-down. Find “BD Custom Contact Form Code”. This should open a BLANK PHP file.
6) On the editor, copy the following code and paste it at the bottom of the file (before any ?> closing tags) so that it looks like this:
Save the PHP file by clicking Update File:
You should get this message next:
7) Go visit your Contact Form for a listing now.
8) You should see a Phone Number visible on the form!