OS X Mavericks :: Delete Second User That Migration Assistant Has Made Into Primary User?

Just got a new MacBook Pro, wanted to transfer my data from the old (2010) MBP. I've done this dozens of times before, but always manually, via Finder copies from external hard disks, etc. This time I decided to try the Official Method, using Migration Assistant. After numerous tries, I couldn't get Migration Assistant to work between the two MacBook Pros (both running 10.9.3), even with Apple's assistance. So I decided to try it with a MacBook running 10.6.8. It worked (though poorly; Migration Assistance needs some serious repair), which was useful (now I know that Migration Assistant works, and it's not a problem with the cabling I was using, but something in the old MBP).  But now I have two user accounts on my new MacBook Pro, which I don't want, plus the added account has now been made the primary account, with (some) data from the previously primary account moved to it. 

So I want to delete the new, added, now primary user and return the MBP to its former, pristine state. So I have to go through all the data (fortunately there isn't much; both the new MBP and the MacBook were only recently set up) that's been moved from the original account to the added account, move it back to the original account, then delete the added account (if I can). This was somewhat complicated by the fact that the ~/Library folder is now invisible by default, but I figured that out. However, what I'm wondering now is, when the second, added account was made the primary account, did it assume all attributes of the former primary account, including its number? I know that user accounts in Mac OS have numbers, like 501, 502, etc.

How can I see the numbers of these two accounts? And if the added account is now number 501, when I delete it, how I can I restore the number 501 to the original account? Or perhaps I should just return the new MBP to its factory state, and start over? But I can't, since it didn't come with any Install DVDs (nor indeed, with an optical drive). (I've been out of touch with the Mac world for several years due to illness, am only now learning about the changes since 10.6, which I'd been using until less than a week ago.) I can wipe the MacBook Pro and reinstall 10.9.3, but that might lose some information specific to this computer that came with it.