I would say, the DISA can be removed as many times as you like now. As far as the fitment, just be sure you have ALL the old gasket material out -- then once you get the material out and fit the new o-ring I took some time to compress it into the valley --- meaning I just didnt pop it on and stick it in - ha! yea...I know....
anyway, even if you can see a little bit, I doubt your having any leakage, so, as long as it does not bother you, I would suggest to leave it alone
what trouble did you have with the boot? I did mine also when I did the DISA, it was a tad tricky but got it, --- did you have issues with the hose clamps? If so, they are put on 'backwords' from the factory, and you have to get to the heads from the bottom, or, get an extension, stick your hand under and go up (meaning you dont need the car up in the air, but that may be easier) I had mine apart NOT on a lift when I discovered this, so I had to make do, -- it took me about 90 minutes to take it apart and then 5 minutes to put it back together with the heads of the hose clamsps facing up. I had a hole in my lower, so, it had to be done. When you are putting it back together, just make sure everything lines up snug, or else you will be doing it all over again !