If I haven’t upgraded my version of Xojo since the last update to a Web CGI app, and I haven’t updated any images that app uses, can I safely assume that the only file I need to upload is the new executable file? That is, it looks like I wouldn’t need to upload freshly created Libs and Resources stuff. Is that right?
I couldn’t say for certain. If you have FTP access, grab a trial of Beyond Compare and point it at the ftp site and your build folder. You can get it to perform byte comparisons if needed.
A small detail : if your app is running when you perform your replacement of the executable, the older one will keep running unless you kill the process.
See this article from Phillip Zedalis about that very subject :
http://www.dev.1701software.com/blog/2013/09/08/upgrading-xojo-cgi-apps
For the rest, I usually upload everything, as it comes from a build. That way, I am certain all dependencies are right.