Writers are usually advised to target their work at a particular market. Up to a point this makes sense. If a magazine only accepts certain genres or lengths, or has a dislike of present tense narrative, it's usually wasting your time and theirs sending them things that don't fit. Most competitions have strict rules and often have a theme, but are more flexible with regard to style. How far should you go in adapting what you write to fit the requirements of editors and competition organisers/judges? 
Sadly, although adhering to the submission guidelines or rules will usually give you a better chance of being accepted or winning, the odds will still be against you. You need to retain your own 'voice' otherwise you're just trying to be a clone, and if your writing is the same as all the rest, how will it stand out enough to be chosen?
My advice would be to make sure that you're still satisfied with the piece and that it still says what you wanted it to. Although each person is an individual and unique, there are millions of people on the planet. Work that is well-written is bound to find readers eventually.