Is possible to use a HTTPS: resource in a URLBuilder in Yahoo Pipes?
I have used a HTTP: easily, but when I change it to HTTPS: I get an error.
You are currently stuck. As of 2/09/09 at least, Yahoo Pipes does not support https.
There is the possibility of setting up your own proxy server to do the SSL fetching for you and re-serve the content over http, but it's not something I've ever tried.