Assuming in
and Keyref
only appear once, and |
never appears, then:
@echo off
setlocal enableDelayedExpansion
set message="The key sequence '1' in 'http://www.myschema.com/dummy:dummy_PK' Keyref fails to refer to some key."
set "message=!message: in =|!"
set "message=!message: Keyref =|!"
for /f "delims=| tokens=1,3" %%A in ("!message!") do set "message=%%A %%B"
set message