Here’s a quick custom action tutorial. Zoom to midi items, quantise, then humanise. I really like the humanise function in Reaper, as it avoids quantised notes layering up exactly on top of each other, and gives the mix a bit more breathing room.

John Garden
Musical Director - Scissor Sisters 2004-2011 Alison Moyet 2001-2003/2013-2014
Composer - Tales of the City the Musical