It will only ever really affect you if you bind every single day for many years. And what changes is just the fat, so you might get saggy boobs at most. Again, that is if you do it for a long time, all the time and tightly.
Otherwise, there really isn't any short or long term affects within the basic cosplay world. At most there is the chance of discomfort due to improper use of materials or heat etc. But most of the time nothing ever serious, especially if you take care of yourself.
So yup, for a couple times a year...you will be just fine
(Of course there are exceptions if you have a prexisting condition of some sort, but I am talking about healthy chests at the moment)