Explicitly specify behaviors that can change
During the creation of components, Terraform will use the default options of the provider that you are using, if these are not predefined. It's important to acknowledge the default components in use and define them in Terraform, as it's possible that you need them in the future and default options may be modified by your chosen providers with no notice, resulting in two different component sets or changes in the properties of the components.
‒ https://www.endava.com/en/blog/Engineering/2019/11-Things-I-wish-I-knew-before-working-with-Terraform-II (emphasis mine)
How to update a module
If a module is already downloaded, Terraform won't recognise that a new version of a module is available. With terraform get it is possible to download the modules, but it's recommended to use the -update option to force an update.
terraform get -update
Can I modify a machine provisioned with Terraform?
Yes, you can - only those changes will be lost on redeployment, since Terraform won't be able to track them.
Using Terraform and then making changes with other tools besides Terraform (eg Web Consoles, CLI Tools, or SDK) will create inconsistencies and affect the stability and confidence of the infrastructure. (...)
Any of the manual changes won't be on the defined VCS, so if a redeployment is required, those changes will be lost.
‒ Julian Alarcon, https://www.endava.com/en/blog/Engineering/2019/11-Things-I-wish-I-knew-before-working-with-Terraform-I