[ericgtr]

There are a lot of ways you can do this, it's really a matter of preference. Here is a way to add it to the Edit Profile section of the usercp.

add a phrase:
Phrase Type: Global
Varname: refer_id
Text: Your Custom Referall ID is

add another phrase:
Phrase Type: Global
Varname: refer_id2
Text: Custom Refferal ID

In your modifyprofile template find:

value="$vbphrase[edit_email_and_password]" name="gotopassword" />
					</td>
				</tr>
				</table>
			</fieldset>

Add after:

<!-- Custom referral ID -->
<fieldset class="fieldset">
<legend>$vbphrase[refer_id2]</legend>
<br />
$vbphrase[refer_id]: 
<br />
<a href="$vboptions[bburl]/$vboptions[forumhome].php?referrerid=$bbuserinfo[userid]">$vboptions[bburl]/$vboptions[forumhome].php?referrerid=$bbuserinfo[userid]</a>
</fieldset>
<br />
<!-- Custom referral ID -->

Here's what it will look like..