Lakka is just like booting another payload and payloads are always temporary, so you just do as said above and boot Hekate when you want to boot Lakka, then Lakka can boot to RCM and you send your Atmosphere payload to get back to it now. You could also add Fusee Starter to your homebrew where you can boot directly to Lakka from your main Switch menu which saves you having to send a payload to get to Lakka, one day we may get reboot to payload from Lakka so you can switch back and forth without sending any payloads.