Reaper's notation is really great, I use it to compose and orchestrate everything I do, then I just export via xml into Dorico and polish it there.
Part of its greateness is scripting, it can multiply usability greatly, so I really recommend learning to script. You can see how all notation events' code look in the event mode or in the RAW MIDI data viewer.
For inserting an empty MIDI item, there is this function
https://www.extremraym.com/cloud/rea...MIDIItemInProj. For a "specific" MIDI item, where would to get it from?