If I understand now, you want to be listening to the music without the MIDI, with a MIDI editor open. You input notes matching what you hear, and you want to hear them only when you input them just so you know they are right, but you do not want them to play back as you move through the song.
I can see why you want this workflow, it makes sense.
The reason this is very difficult is the flow of data.
The only solution I can think of is:
Change the MIDI editor channel to 16, or any channel that you are not using in your MIDI already.
Insert the plugin JS: MIDI Tool v2
Set Output Velocity Max to 0
Set input to channel 1
Click bypass in the top right corner
Now click 'Param' and it should say 'Last touched: Bypass'
Click parameter modulation, and set it as so:
Track audio channels 3+4
Min volume -60
Max volume -60
Attack 0
Negative direction
Move the baseline value all the way to the right
Finally, route the audio track to the MIDI track to channels 3/4:
Now when you press play, the audio is going to be sent to the MIDI track silently (because channels 3/4 will not play through the master track) and this audio is going to make the MIDI Tool v2 plugin
unbypass. It will now turn all of your MIDI to velocity 0, muting it. However channel 16 is still free to be played.
Now you can leave all your tracks unsolo'd. When you enter MIDI notes, they will play back, but the MIDI on channel 1
will not play unless you mute the audio track.When you are ready to commit them, select them and right click and set channel to 1.
If you want to play both tracks at once, move the MIDI Tool v2 FX to after the VSTi / AUi plugin making the sounds or move Output Velocity Max back to 127.
(Reaper... anything is possible....)