可以：
John had done his work and ( had ) got changed for home when his boss stopped him for some more work
had done AND had got changed (两个过去完成时) + when + 从句的“一般过去时”
可以：
John had done his work and ( had ) got changed for home when his boss stopped him for some more work
had done AND had got changed (两个过去完成时) + when + 从句的“一般过去时”