Agents that instrument code in modules may need to augment the set of modules that are read, exports, or services used/provided. We need to add a function to JVM TI to do this, RedefineModule has been proposed. A possible starting point is:

struct _jvmtiModuleExports {
    const char* pkg_name;
    jint target_count;
    const jobject* targets;
}

struct _jvmtiModuleProvides {
    jclass service;
    jint provide_count;
    const jclass* impl_class;
}

jvmtiError (JNICALL *RedefineModule) (jvmtiEnv* env,
  jint reads_count,
  const jobject* reads,
  jint exports_count,
  const jvmtiModulesExport* exports,
  jint uses_count,
  const jclass* uses,
  jint provides_count,
  const jvmtiModuleProvides* provides)

Implementation-wise then this function will likely just call the supporting methods in jdk.internal.module.Modules. The bulk of the effort will therefore be tests rather than implementation.