This is sound advice. Unless it's absolutely necessary, I try not to tweak my reservation with MSC after I've booked. You will receive an email with an updated reservation confirmation a few minutes after you complete your phone call with customer service. More than once I've looked at the new document and discovered a change or an error unrelated to the issue I called about originally. It's just a weird thing with MSC that I've learned to accept and work around. Now, having said that, to me it would be worth the risk to be able to move to an angled or larger balcony.
Let me give you a couple of examples of the relatively minor (but still somewhat annoying) issues I've had after contacting customer service for a change: 1) emailed existingreservations to add my military discount - got the discount but they changed my fare to the current "sale" which was higher than the original fare I booked. 2) I requested to change my cabin from port side to starboard side (same YC category) - I noticed that I lost the OBC I had gotten as part of the promo going on when I originally booked.
The customer service agents are always very helpful, it's just an oddity that, like I said, I learned to live with by avoiding messing with my reservation.