What kind of DRS rules are you talking about?
Affinity, anti-affinity, VM-Host?
And are you only talking about DRS or also SDRS?
When you add a rule after a VM is created, DRS (or SDRS) should take care of the rules.
A script that check at regular intervals of there are rules for each VM should be sufficient.
In fact, if I remember correctly there is a similar thread (with a solution) in this community.
Try using the Search function.