This might be DFTW or disney photography rules but as I've done it (disney bride in 2012) and other disney bride friends have as well on castaway cay I was not stopped or questioned one time by anyone. As you can also see from the photos we went on an excursion in our wedding gear and again was not questioned or stopped ever. Disney world is very strict but luckily disney cruise isn't the same. There should be nothing stopping the OP from doing trash the dress!!! Like I said amazing experience!!!
And when the term trash the dress is used. Doesn't mean the dress is really being trashed. Mine had feathers and all and it still looks new to this day. Never really trashed it