First you have to understand that a url is not sent the way you type it in http.
So the request actually looks like this :
GET /privatedata.html
Host: secure.example.com
This request is encrypted with SSL if you enter the url with HTTPS:// and is sent in cleartext if you don't use SSL.
So, what the offloader will do is simply decrypt the traffic and whatever the request will send it in cleartext to the server ip address.
The offloader can't change the content of the request. However, it can add some lines in the header.
Also, instead of just transmitting in cleartext, the loadbalancer can re-encrypt so the communication between offloader and server is also SSL.
Again, the request (see above) does not change.
Gilles.