Vatican City, February 20 - A senior Vatican figure said on Wednesday that Pope Benedict XVI has the power to change rules followed for the selection of his successor, and explained why the conclave of cardinals is likely to commence mid-March, but could begin days earlier. ''The Holy Father is the only one who can intervene in the legislation regarding the conclave,'' said Ambrogio Piazzoni, deputy prefect of the Vatican Apostolic Library, in a briefing at the Vatican press room on the history of Vatican conclaves. ''If Pope Benedict (XVI) were to decide on new rules at 19:59 on February 28, those would be the ones to be followed for the new conclave,'' Piazzoni explained. Piazzoni added that according to the current rules, ''the cardinals present in Rome will wait 15 days for the arrival of all the others. This could signify that if all the cardinals are in Rome, there is nothing to wait for''. The Vatican has yet to announce a date for the beginning of the next conclave, but Pope Benedict XVI is stepping down at 20:00 on February 28. Piazzoni's statement indicates that while it would be customary to begin in line with mid-March forecasts, the Vatican could commence the conclave earlier. ''The latecomers are admitted if they arrive after the conclave has begun but not yet concluded,'' Piazzoni added.