The special dispensation follows discussions between the RFU's Disciplinary Officer and London Irish Managing Director Conor O'Shea about the participation of Todd in the special charity match between a London Irish All Stars XV and the Barbarians which will raise funds for former Exiles player Jarrod Cunningham, who was diagnosed last year with ALS, a rare form of Motor Neurone Disease.
"I received an approach from Conor, on behalf of Jarrod, for Robert to play in his benefit game," said Horner. "They have been close friends for a number of years and the appeal was made for Robert to be given special dispensation to play for London Irish against the Barbarians.
"We were all mindful that Robert still has 14 days of a three-week ban to serve. However, I have decided that it is only right, in these exceptional circumstances, that Robert be given permission to play in the game, which we hope raises a substantial sum for Jarrod."
Todd's ban will be completed on March 19.
London Irish All-stars v The BarbariansKick-off: Thursday, March 6, 19.45 GMT, The Stoop