Blackstone Group, one of the most coveted employers on Wall Street, is throwing out a key section of its recruiting playbook in a bid to improve its hiring process and increase diversity.

The investing giant and its private-equity peers have long engaged in a yearly race to pluck junior investment bankers already trained in spreadsheet and PowerPoint wizardry from firms such as Goldman Sachs Group Inc. and Morgan Stanley. The prize for those lucky enough to make the jump: entry-level jobs that can pay as much as $300,000 a year at some firms.