I don't think we can set it per specific planet right now, but if you go to Settings > Automation, you can set an automatic global count for all of your planets, as well as FRD them.
I'll note that Remains Rebuilders are being removed next update (and your Command Stations, plus the new Battlestations/Citadels will do it instead), and Engineers are essentially per-planet cap, so you can just max them out everywhere.