shell> ./tools/tpm configure alpha \
    --hosts=host3 \
    --backup-method=xtrabackup-incremental

This will apply the --repl-backup-method option to just the host3 server. Multiple hosts may be given as a comma-separated list. The names used in the --members, --slaves, --master, options should be used when calling --hosts. These values will override any given in tpm configure defaults or tpm configure alpha.