iRule redirect from sports.test.co.uk/ioks/* to www.test.co.uk/ioks/*

You can use either strategy, but if there is a specific order you want them to be processed there is a consideration. If you added it to the existing rule you can definitely order the evaluation like you did above with an elseif. If you wanted a specific processing order with putting it in a new iRule you would want to use priority. https://devcentral.f5.com/wiki/iRules.priority.ashx. Also, if you want to retain the full URI you will have to do something like below. Below if the new iRule with a lower priority so it will be evaulated after the first iRules HTTP_REQUEST.

when HTTP_REQUEST priority 600 {
    if { [string tolower [HTTP::uri]] starts_with "/ioks/"}{
        HTTP::respond 301 noserver Location "https://www.test2.com[HTTP::uri]"
    }
}