A man who used false papers to collect welfare benefits stayed in character when he was arraigned yesterday in Suffolk Superior Court and signed paperwork using the identity of one of his victims, prosecutors said.Clei Sandoval-Arias, 29, was identified with the help of the U.S. Inspector General’s Office, which used contacts within the government of the Dominican Republic to verify his identity.Sandoval-Arias, however, insisted on signing probation forms and other paperwork yesterday using the name of one of his victims, prosecutors said.