How to add an unverified module on cloud-init

Question

It is mentioned everywhere that I need to add unverified_modules: ['module-name'] if I want to add module-name that is not verified for my distro where I am running cloud-init. However, it is not mentioned where I should add these lines. Should I add it to the userdata that I am injecting? Or should I create a file under /etc/cloud/cloud.cfg.d and add these lines over there? Please help!

I am trying to use resolv_conf module that is not supported on Ubuntu for cloud-init. Here, I am trying to update the /etc/resolv.conf file. What is the right way to do it? Add it as an unverified_module or run a script to do this?