Application is open

Yes it is and I have just sent an email to ALJ Application Desk that I want to change my geographic availability to any of 150-something places they listed. Previosuly i had less than 30 and more than a half were never the ones they were hiring so far (since 10/07). Of course, I am on that register...
Just as a note, I have been monitoring this forum since its inception but I never registered - sorry - however, I felt somehow that it is time to do so.
Good luck to new applicants, old ones who didn't make the register last time for whatever reason, and all of us who did but pretty much for nothing and will face new competition in the months to come!

Does anyone know if you can reapply if you are already on this register?

I am reminded of the situation where you get your iced tea just right, drink half, and the helpful waiter fills it back up - thereby ruining the mix. Although I suppose that there were locations which no longer had at least three applicants, even that scenario is unlikely in light of the number of applicants who listed every location -- even those most of us would consider G*d-forsaken. Hence, the reopening of the process appears to confirm what many suspected all along: that these selections were predetermined and that there were "ringers" who, for whatever reason, either did not apply in time last time or had some sort of error (such as a missing bar number). I did not gripe about this before because one had, at best, a one-in-three chance, and therefore one's nonselection did not mean that the process was unfair. But with more than 400 still on the register, and the new posting reaffirming that the "vacancy announcement is being reopened so that the current ALJ register can be refreshed with additional qualified applicants," it appears that those of us remaining on the Register are qualified. To the extent that the previous hires from the Register "skimmed" the higher graded applicants, OPM will now "refresh" the register with additional higher graded applicants, and those of us with fair-to-midlin scores (and disabled from increasing those scores because less than a year has elapsed) will again find numerous applicants ahead of us on the Register. The process is now clearly a sham, unless OPM has been informed by SSA that it intends to hire several hundred more ALJs and hence, the 400 hundred remaining is an inadequate pool of candidates.

That is certainly a possibility but not a high probability. I can see the first offer being for a place that one would never accept for whatever reason but it's not nearly as likely, from the standpoint of theory of probability, to have that with the second one as well. Now, I admit, Murphy's law would say opposite.
On the other hand, yes, I personally know at least one person who would not go out of her town pretty much to any other place due to family reasons and that reduces chances to get hired drastically. And don't get me wrong, IMHO that's a legitimate reason for picking a very limited number of places to serve. My logic is different. Not that I would like to serve absolutely anywhere. I don't want that badly to be an ALJ. But I made a mistake first time around not choosing that option (and and all cities, so to speak), as every sitting ALJ told me afterwards, and now I corrected it. If they offer me a place to serve that I wouldn't accept for anything I will tell them no. If they offer me a place I am not really happy about it I will aceept and do "time" (at least 2 years) as almost every ALJ I know had to before got transferred where s/he wanted to be in the first place.
Again, I am aware this will not work for everyone, maybe not even most, but having no opportunity to reapply (and retest/rescore) at this time, what else could I do? Obviously whatever score I got and places I picked didn't work so far and with more new names and scores on the register fairly soon it is clear to me it would be definitively an end to expectations to be an ALJ. Something had to be done and this is the only thing that I could do. Whether it will pay off well, that is to be seen. Quite possibly it will not. But at least I feel I tried.

I too made sure to get my geographic changes in first day - it appears when the application closes, the time to change your locations also closes for those on the list.

I have added a lot more places to my availability, but still picked only about 2/3 of the available. I was rushing so much when doing the application, I only picked places I was sure I would want to go. I didn't even know where half of these cities were. After reviewing, and seeing which were next to other cities I was interested in, etc., I have been able to expand my list realistically. (It helps that I am unmarried and have no kids).

Is anyone else expecting the application to close today? 1250 took about four or five days last time, didn't it? And people were less prepared and a weekend was involved.

Any thoughts on when the amended geographical preferences would go into effect? I should expect that it would be no later than 13 August, the day that the listing "officially" closes.

The exact date doesn't really matter. What is important is that the amended locations will be in effect for the next certificate, whenever that will be. Pix.

But since SSA is extremely unlikely to request a cert before OPM completes "refreshing" the register, the point is moot, and I would listen to Pix. Rinse, repeat.