In my short writing career, I have withdrawn a story from consideration a grand total of twice. Both times were instances of discovering a divergence of opinion on issues of race/sexuality with the editorial staff. And I haven't submitted anything to either of those markets since.
I mention this, not because I'm such a crusader for equality, but because every now and again I see someone asking about making a simultaneous submission on the sly. In other words, they have multiple markets they wish to submit a particular story to, both of which request "No Sim Subs", and one of which has a deadline/really slow response time. Usually the question is "Can't I just withdraw the story from one market if it were picked up by the other one?"
The short answer is: Yes.
Naturally, there is nothing to prevent you from sending your story to every market at once. There is nothing to prevent you from withdrawing a story from a market at any time for any reason - whether it be that you subbed to more than one market and had an acceptance or you decided it needed more revisions or because you realized the editor was anti-banana and you're pro-banana and you don't want him/her publishing your story anyway.
But there are a couple of things you should keep in mind when considering withdrawing a story. (Or considering putting yourself in a position where you might have to withdraw a story.)
Firstly, once a story is withdrawn it cannot be resubmitted to the same market at a later date. Withdrawing a story is like giving yourself a rejection notice.
Secondly, while it may seem like an editor won't know why you decided to withdraw a story there are a limited number of possibilities.
1: You submitted something that wasn't ready.
2. You submitted something to more than one market despite being asked not to.
3: You found a market that pays more/has more exposure/whatever and you want to try them first.
4. You have decided you don't want to work with the editor.
None of those possibilities is likely to make the editor/slush-crew think very highly of you. Some won't care enough to remember it the next time you might submit something (this is assuming that either #4 doesn't apply or you've changed your mind about the anti-banana stance of the editor-in-chief). Some will.
So, my rule of thumb is: Don't withdraw a story unless you have no intention of working with a market/editor ever again.
My second rule of thumb is: Don't put yourself in a position to NEED to withdraw a story.
This means, No Sim Subs (unless a market says it's okay) and Always Be Certain a Story is Ready To Sell.