ofxmerge is a small tool that merges 2 or more OFX files.
ofxmerge
To install:
$ go build -o ./ofxmerge .
To merge with output of new OFX file being sent to standard out:
$ ./ofxmerge file1.ofx file2.ofx
git.compounddata.com/ofxmerge
ofxmerge is not actively developed.