Record notes to different MIDI channels

Easy way is to use a DAW that runs on your operating system and that supports scripting such as Reaper  ( Windows, Mac OS, Linux)  or Logic Pro ( Mac OS)   
Then ask Gemini or ChatGPT or DeepSeek to write your script.

For instance here is a  script in Reaper that does what you want :
Create a new action in Reaper (ReaScript)   and use Python as the language
Copy paste the following code ( here generated by Gemini ) in the action
In this case the cut off pitch is C4 , and notes below will be written to channel 1, and notes above to channel 2
Load or Record your midi file  in a track , and run the action. That's it.

In this example you transform the code after recording and perform the loop on midi events.
You could also write a script that works in realtime , intercept the note-on events and depending on the note on pick value assign a midi channel.

============================================

# SCRIPT: Split MIDI Notes by Pitch and Assign Channels
# LANGUAGE: Python
# AUTHOR: Gemini (Adapted from Python pretty_midi logic)

from reaper_python import *
import struct

# --- CONFIGURATION ---
# MIDI Note Number (0-127). 60 = Middle C (C4).
PITCH_CUTOFF = 60

# MIDI Channel assignments (1-16)
LOW_NOTES_CHANNEL = 1
HIGH_NOTES_CHANNEL = 2
# Note: MIDI channel is 0-indexed in the MIDI message (0-15).
# So Channel 1 is 0x00, Channel 2 is 0x01, etc.
LOW_CHANNEL_BYTE = (LOW_NOTES_CHANNEL - 1)
HIGH_CHANNEL_BYTE = (HIGH_NOTES_CHANNEL - 1)
# ---------------------

def main():
    # 1. Check for selected MIDI item
    item = RPR_GetSelectedMediaItem(0, 0) # Get the first selected item
    if not item:
        RPR_ShowConsoleMsg("Error: Select a MIDI item first.\n")
        return

    take = RPR_GetActiveTake(item)
    if not take:
        RPR_ShowConsoleMsg("Error: Selected item has no active take.\n")
        return

    # 2. Open MIDI item for editing (required for modification)
    RPR_MIDI_SetItemTakeChannelMap(take, -1, 0) # Clear channel map to avoid conflicts
    RPR_MIDI_SetItemTakeChannelMap(take, -1, 0)
    RPR_MIDI_SetItemTakeChannelMap(take, -1, 0)

    RPR_MIDI_SetItemTakeChannelMap(take, 0, 0)
    RPR_MIDI_SetItemTakeChannelMap(take, 1, 1)

    # RPR_MIDI_SetItemTakeChannelMap(take, LOW_CHANNEL_BYTE, 0) # Assign Channel 1
    # RPR_MIDI_SetItemTakeChannelMap(take, HIGH_CHANNEL_BYTE, 1) # Assign Channel 2

    RPR_Undo_BeginBlock2(0) # Start Undo Block

    # 3. Iterate through all MIDI events
    # index: 0 is the starting index.
    # We use a loop and increment the index until RPR_MIDI_EnumItemInTake only returns 0
   
    # event_idx: the index of the event
    # is_selected: whether the event is selected
    # is_muted: whether the event is muted
    # ppq_pos: position in PPQ (Pulses Per Quarter note)
    # message: the raw MIDI message bytes
   
    event_idx = 0
    while True:
        (ret, take, event_idx, is_selected, is_muted, ppq_pos, message) = RPR_MIDI_GetEvt(take, event_idx)
       
        if ret == 0:
            # End of events list
            break

        # Check if the message is a Note-On event (Status byte 0x90 to 0x9F)
        # Note-On message status byte: 0x90 + channel (0-15)
        # We only care about the first byte's high nibble (0x9_)
        status = message[0] & 0xF0
       
        # Check if it's a Note-On event (0x90) and not a Note-Off with velocity 0
        if status == 0x90 and len(message) >= 3 and message[2] > 0:
           
            # Message is: [Status+Channel, Note/Pitch, Velocity]
            pitch = message[1]

            if pitch < PITCH_CUTOFF:
                # Assign to LOW_NOTES_CHANNEL
                new_status = 0x90 | LOW_CHANNEL_BYTE
            else:
                # Assign to HIGH_NOTES_CHANNEL
                new_status = 0x90 | HIGH_CHANNEL_BYTE
               
            # Create the new message with the modified channel
            new_message = struct.pack('BBB', new_status, message[1], message[2])
           
            # Update the event in the MIDI item
            RPR_MIDI_SetEvt(take, event_idx, is_selected, is_muted, ppq_pos, new_message)

        # Increment index to get the next event
        event_idx += 1

    # 4. Update and close the MIDI item
    RPR_MIDI_Sort(take)
    RPR_UpdateItemInProject(item)
    RPR_Undo_EndBlock2(0, "Split MIDI Notes by Pitch and Channel", -1)
   
    RPR_ShowConsoleMsg(f"\n✅ Successfully split notes in the selected item!")
    RPR_ShowConsoleMsg(f"   - Cutoff Pitch: {PITCH_CUTOFF}")
    RPR_ShowConsoleMsg(f"   - Notes < Cutoff assigned to MIDI Channel {LOW_NOTES_CHANNEL}")
    RPR_ShowConsoleMsg(f"   - Notes >= Cutoff assigned to MIDI Channel {HIGH_NOTES_CHANNEL}")

main()