Updating current internship on resume?

Just update it with what you have been doing. Try to have at least one process you were involved in pretty significantly, and know how to tell this "story" in your interviews, should you decide to recruit again in the fall. It doesn't have to be the biggest merger in history; in fact, talking about a deal that wound up failing wouldn't hurt you at all in my book (lends itself easily to follow up questions that try to see how much you really know, i.e. why did the deal fail, and what could you have done as an analyst to get a better result if a similar situation comes up? what about if you're a senior banker running the deal? etc.)

In general, most people reviewing resumes assume the same thing when they see IBD SA on someone's resume (worked on comps, DCF's, LBO analysis maybe, perhaps capital raise deals, etc.) but what's going to distinguish you in the end is how well you interview, and the truth is that FT interviews aren't significantly different from SA interviews, except you might be asked to explain a deal you were on and questions might go a little bit more in depth. I've never heard of someone getting a modeling test in an analyst interview, so as long as you really understand the concepts, you should be ok for these interviews. On the other hand, going through a model goes a long way in understanding how to actually implement concepts in practice, so if you don't get staffed on a deal, what you might do is to ask your analyst if you can see a model from a past deal, and then make a copy, and spend some time playing around with the inputs and coming up with rationale for why certain assumptions are what they are.