HTTP Response Rewrite

If the header is always the same you can simple do the following:

when HTTP_RESPONSE {
    if {[HTTP::header exists "X-Storage-Url"]} {
        HTTP::header replace "X-Storage-Url" "http://example.com/v1/AUTH_example"
    }
}

This is quicker than trying to for a search and replace in the value of the header.

If the header is dynamic then the following would take the header and split it into a list using "/" as a split character, replace the first element in the list with "http:" then replace the header after joining the list.

when HTTP_RESPONSE {
    if {[HTTP::header exists "X-Storage-Url"]} {
        set xStorageUrl [split [HTTP::header "X-Storage-Url"] "/"]
        lreplace $xStorageUrl 0 0 "http:"
        HTTP::header replace "X-Storage-Url" [join $xStorageUrl "/"]
    }
}

You can also do this with a regular expression however as much more resource intensive recommend this only if the volume is going to be low and you do not have a lot of iRules running on the F5.

when HTTP_RESPONSE {
    if {[HTTP::header exists "X-Storage-Url"]} {
        HTTP::header replace "X-Storage-Url" [regsub "^https" [HTTP::header "X-Storage-Url"] "http"]
    }
}