Also if your providers + OS support cloud-init, then you can express a fleet of instances which run this sort of script at boot time in something like Terraform pretty easily. Switching clouds becomes "uh... what does <provider> call their <size> instance again?"

Alternatively, pre-baking cloud images that have already run such a script and are ready to boot becomes pretty easy with a tool like Packer.

Though, as the underlying OS changes, you'll need something to validate your scripts' functionality against, and a tool that's a little more declarative might make them less fragile to those changes.