The phrase "Si qui autem ante ordinati sunt subdiacones inter subdiacones habeantur, ita ut manum non imponat aut sacra non contingant." is difficult to interpret. It describes just a result of degradation, because subdeacons normally do not impose hands or touch the sacred things, or it orders the prevention of the penitent subdeacons from fulfilling some of their normal obligations (Weckwerth 2004: 135-136).
For more on the ecclesiastical legislation on public penitents see May 1961: 252-268.