I doubt you could. Now if you double posted and it got merged...it's theoretically possible that the merging plugin has permissions to ignore that limit, but I am uncertain of that. It depends on what context it runs in; in respect to the original vB code.
Now it's entirely possible that it will truncate the resulting post when merging.
Needless to say, there's no reason you should be able to double post without permission from the staff. Unless the rules for that section say you can double post in a certain situation. (double check to make sure you're in that situation) then the rule generally applies that you shouldn't double post. I'm not certain about the auto double-post merging plugin being active. It may indeed be active selectively or not at all.
EDIT: Cool~ no more limit \o/ Can you take the limit off the signature too? (it limits to 25 lines)