local command based on timestamp before another file?

Theres probably a better way to do this, so please tell me.

for a given linux host, the netfilter rules for ipv4 and ipv6 are the same, except for when i run it in vagrant, because i dont to cut off my vagrant host.
10.0.2.15 is the ip address vagrant gives you, and before running ansible, i have a shell provisioner that sets the default gateway to another vagrant box acting as an isp.
this makes that interface ansible_default_ipv4.interface. since its the same interface for v6, this is how i generate those rules.

grep -v 10.0.2.15 rules.v4 > rules.v6

i dont want to forget to run that. is there a way trigger a local command based on the timestamps? i realize in this case, it would be trivial just let it always run, but it got me curious.