URL Host rewrite then pool selection based on URI

Your question isn't very clear.

Changing the HTTP Host header has no impact on the URL displayed in the browser - it just reflects the address of the page currently being displayed.

Changing the host header in HTTP_REQUEST may change the content delivered by the pool member, if the pool member is serving multiple sites distinguished by Host name.

However, if the pool member returns a redirect, it may redirect to the host specified in the Host header, which will change the address in the browser bar:

browser requests http://bob.com/tobee

pool_A member responds with a 200 OK

- browser bar displays bob.com/tobee

browser requests http://bob.com/nottobee

pool_B member responds with a 302 Redirect to http://www.bob.com/nottobee/

- browser bar now displays www.bob.com/nottobee/

Use the Browser developer tools Network tab to determine if multiple requests are being made for each of these cases.