Here's a list of Reaper API's that give applications and scripts access and control of Reaper.

https://www.extremraym.com/cloud/reascript-doc/

So if I want to add a project marker using Lua script language I use the API:

integer reaper.AddProjectMarker(ReaProject proj, boolean isrgn, number pos, number rgnend, string name, integer wantidx)

To do this in BB I made the Chord Picker Tool that uses AutoHotKey GUI to send the keystrokes and inputs, if BB goes 64bit it will still work same with APIs as long as the 64 bit has the same API functions as the 32bit.