I just noticed the gibberish in Post #36: "Renewal of Extension." Who is thinking up this confusing terminology? People who have permission to stay in Thailand can extend their stay. When that period of stay expires, they can apply for another extension. They cannot renew the extension that they have. For those who would argue that ambiguous language doesn't matter if people kind of, sort of, understand what they mean I would reply as I have to my writing students over the years: you may understand what you mean but your reader may not. There is no substitute for precise, unambiguous language and it is the writer's responsibility to make his meaning clear.

There is nothing wrong or incorrect in saying that one is renewing an extension of stay. One is applying to extend the extension, to continue (with), and renew is a perfectly acceptable verb to use.

I guess that it is possible to say that you are renewing your extension but that is not what actually happens, is it? You present an application for a new extension of stay with all of your supporting documents and then a new, completely separate extension of stay is stamped into your passport. Your previous permission to stay expires on a certain date. You need a new extension of stay to take effect when your previous extension expires. Why be ambiguous when you can be precise?