You can use Biab SGU MGU etc.. to Reaper Region Chord Names ...
then this will snap all midi notes in selection to the chord(region name) notes.
Make sure you have SWS extensions installed.
It will keep any existing keyswitch notes at the same note.
You can then import back to Biab.
There are also scripts to create a midi track snap guide from chord or scale notes, as you can see in the gif below.

remove .mp4 ,unzip and install script in Reaper.
ReaTrak Biab SGU MGU.. to regions.zip.mp4

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ReaTrak Biab & Plugin in Reaper
Why Worry (all BB).mp3