SPARQL UPDATE should work via Studio. As Zachary mentioned, there is currently no feedback provided to you on success – we have an open issue for this, so you should expect those messages to appear fairly soon – but the operation should still complete. Can you confirm that it truly isn’t completing, and, if it isn’t, can you provide further detail about the operation you’re trying to perform? Thanks!
We don’t currently have a list of things you can and cannot do in Studio, but one of our initial goals is to provide parity with the features available in the web console. That is still a work in progress, but you should currently be able to do essentially everything you could do in the web console right now, except for query management (one of the next features on our list) and schema browsing.