Good discussion here. It's something that I have looked into heavily--I'm an attorney and licensed real estate salesperson... and occasional wholesaler. So there is a whole bevy of potential liability arrows that may be flung upon me and my various licenses. I can tell you how Ohio law regards the situation, but that's only helpful if you are dealing in Ohio property with an Ohio license.
The NAR's Code of Ethics actually draws a more strict line than my state's laws. Article 4 of the NAR Code states that "Realtors(r) shall not acquire an interest in . . . any real property without making their true position known to the owner or the owner's agent." It also requires that this disclosure be in writing and provided prior to the signing of any contract.
As Mark H. said, you're still open to suit, no matter what you disclose. Compliance with state law and other professional standards is going to be a pretty good defense, but you could still amass some hefty legal bills, as he also pointed. But, that's the case whether you have a license or not.
What the license really adds to the equation IMO is unequal footing. As an agent you have special expertise and knowledge that the average homeowner does not have and you are in a general position of trust and esteem as a professional. If you're compliant with all of the laws and other standards, this unequal footing will be the only legitimate basis for suit by Angry Seller down the road. With that in mind, having turned your license in 7 hours before the deal and then re-activating 2 hours after the deal would seem to be more of a detriment than.
That's alot. Hopefully, that added at least a little to the discussion. My basic position though is this: pick a side and stick to it. If you want a license, keep it. If you don't then leave it inactive. In either case, here's the key - disclose your position clearly, do a good job, don't seek any dishonest gain. The golden rule seems to have universal application.