I am assuming the OBXs shown are what the outbound should look like.
I have done some similar things.
I would try using an IF Action if you are on a release of Cloverleaf that has the ‘Contains’ option in the string compare.
I would use a temp variable to set the value for OBX-3 (GDT or IMP) based on the discovery of CONCLUSION. I would do this such that the GDT is the normal and only gets reset when the discovery of CONCLUSION happens.
Be aware the standard (at least beginning with 2.3) does not specify sub-components for OBX-3 yet that appears to be what is being demanded here (assuming & is the sub-component separator in MSH-2).
However you can use sub-component notation in your COPY Action when COPYing the temp variable to OBX-3 to force this non-compliance.
email: jim.kosloskey@jim-kosloskey.com 29+ years Cloverleaf, 59 years IT - old fart.