1. You can maybe try installing both client files in separate locations, then before running your java application run have some script to specify HADOOP_HOME_DIR
and HADOOP_CONF_DIR and point to the specific one you are running your java client against.
1.1 Most likely not, this is not normally tested, since api’s change normally.
2. other than HAR,You can also use open source file crusher utility for concatenating small files into default block sizes of 128 MB.