You could, But there seem to be some 'reserved' words, like "main"
So if you would have the following in a repo file [main] then this definitely will not be acceptable for yum...Have not encountered any other strings which seem to be reserved/not-to-be-used.
Hope this helps.
Tip: always use some self-expanatory names for respositories. e.g. 'main' to me is not advisable besides the fact that it is not accepted by yum.
Instead of explaining it here, see the official Red Hat documentation for this:
(Keep in mind that you can download these pages as PDF files for your later use.)