Traction only sub contract work

Related question. If I wanted to leave a stand trailer on a customers site, would I need to register that as another operating centre on my licence, or would the fact that it would get back to my operating centre on a regular basis mean I could just run it on my current licence.

For clarification I have a licence authorising two tractor units and two trailers but only specify one unit at the moment. So in theory I have a spare trailer slot I could dump at a regular customers site.