change in behavior from v10 to v11 with HTTP:HOST

You could grab the original host value into a variable and base it on that. Otherwise, I'm not sure of a way to get the original once you modify it.

You could update your iRule to something like this:

set origHost [HTTP::host]
set apiHostProd "test.com" 
set apiPoolProd "test.com-81"

if { [class match $cmd equals "api_commands"] } { 
    HTTP::host $apiHostProd
    HTTP::header replace "Host" $apiHostProd
}

switch -glob -- [string tolower $origHost] {
    "*resell01*" { 
        pool $apiPoolProd member 10.7.58.28 81 
    }
    "*resell02*" { 
        pool $apiPoolProd member 10.7.58.29 81
    }
    "test.com" {
        pool $apiPoolProd 
    } 
    default {
        HTTP::respond 200 content { Error Message To Return To User }
        return
    }
}