I hope all is well. Great question. ( from one Adam to another )
So, there is nothing stopping you from updating any number of ADMX templates, or the entire repository, as often as needed, BUT...
Like anything else, there are always considerations that you need to be aware of, as noted below:
Although rare, policy updates may cause issues with older systems in unexpected ways, so testing prior to deployment is always a good idea if possible.
Ensure that your documentation is updated as you deploy, meaning baselines, build docs, BCDR information, images, etc...
Make sure to inform your help desk / support desk function(s), if appropriate, that you are introducing new elements that they may need to support over time.
Take the time to look at third party interoperability issues if appropriate, meaning do these changes potentially impact third party software that the business relies on? and if so, how?
Specifically, with the last part of your question, regarding concerns about the domain/forest level that you are running, the main thing there is just to ensure that you pay attention to the products that you are applying the ADMX files for, and ensure that you are using the appropriate versions of the ADMX files that are meant for the version(s) of the products in question, and that you are not implementing ADMX files for products/versions that you are not using in production.
Having said all that, the ADMX files are not all conveniently available from one master repo, which would be awesomely nice, but they are all available from one general area via a simple search.
Use the following:
This will take you to the Microsoft download site and will perform a search of the global catalog of downloads for all of the available ADMX files for all products currently available, you will then be able to download which ever ones that you may want.
Good Luck, and please let me know if you have any additional questions.