How to do the reverse of bcf merge?
bcftools has the view command which can do this. Create a text file (samples) which has the names of the samples you want, one per line, and then:

bcftools view -S samples merged.vcf.gz &gt; new.vcf


Or, if you're running a shell that supports it, you can use input redirection for a single sample name:

bcftools view -S &lt;(echo "sample name") merged.vcf.gz &gt; new.vcf