I tried to inject it (with pat-inject), no idea if diazo does the same 'checking' when it is a different URL,
[Error] Failed to load resource: Origin http://localhost:8081 is not allowed by Access-Control-Allow-Origin. (index.html, line 0)
[Error] XMLHttpRequest cannot load http://web-01.ufscar.br/ppgees/index.html?_=1522945547107 due to access control checks.
while you are entirely correct to say that it is necessary to have network enabled, it is unlikely to the extreme that the OP could have missed this fact. If you have seen what happens when Lxml block a network access with Plone, it can't be overlooked. It's pretty much a 'in-your-face' message.
I think that your rule is never applied because it conflicts with the behaviour of your theme. If you examine your generated page in the browser debugger, I think you will find your href directly copied by the block copy done by your theme (if it's Barceloneta it works just like that for central content). If there is a way with a simple rule to externally change the behaviour of a xsl copy, I don't know it. The only way I can see is to special case the whole block copy.