If a panel of or the entire Inquiry Commission determines, by a majority vote, that probable cause exists for a charge to be filed, it shall cause to be prepared such charge stating the name and bar roster address of the attorney and facts alleged to constitute unprofessional conduct. The charge shall be signed by a member of the panel which considers the case. It shall then be filed with the Disciplinary Clerk within twenty (20) days. Upon notice to the respondent, the Inquiry Commission may amend the charge upon its own motion, or that of the Office of Bar Counsel, or the Respondent, at any time before hearing or submission by default.