Change Speed Without Changing The Frame Rate?

way to change the speed of my movieclip without changing the frame rate, as it will mess the rest of my animation up. It looks great at 12fps but the rest of my animation is 24fps. I seem to of come across quite a lot of things about gotoAndStop function but I don't know if this would work as the animation is constantly flowing so wouldn't it suddenly jump? I made one petal and applied the following code to it (kindly done by Gu35s) so there are lots of random pretals moving across the screen, it is done in a similar way to how snow is done using actionscript. Here's the code:

var p = 0;
this.onEnterFrame = function() {
mc = this.attachMovie('petal_mc', 'petal' + p, p);
mc._x = tree_mc._x + (Math.random() * tree_mc._width);

[Code].....