URL redirect/rewrite to external site/header change with internal CA.

Trying to understand your requirement, if its redirect - its fairly simple. Mayur has shared the Irule, add it to the VIP of wallyworld setup & the client should be redirected to the internalworld website.

But there's a catch, are the users internal or external ? external users can't reach the internal site unless that's exposed to Internet.

Or are you trying to rewrite the setup, like User should access wallyworld, but transparently the traffic should be sent to internalworld setup, client will always see wallyworld in his browser...

Tell us more about your requirement & the issue you are facing after deploying the above rule.