UPDATE: This does not work! I was able to compile, but the resulting lib was corrupted and caused issues later on (as described in my other thread).
I downloaded deepstream_sdk_v6.1.0_jetson.tbz2, compiled nvmsgconv there with my custom edits, used the resulting libnvds_msgconv.so within my Deepstream 6.2 app and it worked like a charm.
The only difference is that nvmsgconv in DeepStream 6.1 does not allow NVDS_PAYLOAD_DEEPSTREAM_PROTOBUF as an option and does not use schema.pb.cc file to compile.