This will work for both new and existing repository.
Additional Information
The "numProbeThreads = <value>" line does not exist in the bootstrap file. It must be added manually.
Since all NPM domains (BGP, EIGRP, OSPF & ISIS) are build on the same foundation, you can simply add the numProbeThreads line to the bootstrap file of the protocol desired as instructed above to increase the number of discovery threads for that protocol.