I meant using it with different version for each directory - is not possible.
Yeah, you need to edit a lib file to make this happen or wait until next Virtualmin release:
Find at /usr/libexec/webmin/virtual-server/virtual-server-lib.pl
"7.0", 7.1, 7.2, 7.3);
and replace with:
"7.0", 7.1, 7.2, 7.3, 7.4);