For most of the past month, whenever San Francisco 49ers wide receiver Ricky Pearsall stepped into position drills during practice, he was unsure who would join him. Such is life as a Niners receiver this summer when the only constant has been a steady stream of change. From July 18, a few days before the start of camp, through Sunday evening, the team has made 18 transactions at receiver, a mix of signings, releases, placing players on injured reserve or the physically unable to perform list and even a trade. “It’s just definitely not normal,” Pearsall said.