It is up to the user to take "reasonable steps" to find the license. Keeping license notice in each file helps, especially when someone uses part of your code to create something else, and files with multiple licenses are mixed. Such situations are good to avoid, but if someone takes the code, he/she should check licensing and provide proper information in the derivative work.
This is what you will actually find in GNU FAQ, though they make a big issue out of the derivative works:
https://www.gnu.org/licenses/gpl-faq.en.html#NoticeInSourceFile
To modify a lot of VIs, you may use pylabview - if you know how to use use python or bash, you can make a batch to extract, modify and re-create any amount of RSRC files with it.
You only need to make the script which does the modification, ie. add the documentation to one file, and compare extracted XML before and after the modification to get a patch to be applied to all other files.
For the selection - if you don't mind others using it for anything, MIT is a good choice. Though sometimes people say that, and then still feel cheated when someone makes modification to the work and starts making money out of it... if you feel unsure here, you may choose GPL instead.
And if you completely don't care about license and want to mock it a bit, there's always DBAD - it's quite popular for underground tools.