[CentOS] usermod under CentOS

	My wife's PC, running CentOS 6, suddenly quit connecting to the 
Net. Autodidact that I am, I fumbled with all the hard- and software I 
could find or dared try, but did no good. 

	So we lugged it down to our favorite shop. While there, she bought 
a laptop, and asked them to install CentOS and copy all her files from the 
PC (including two books she's written and is trying to market).

	They called to ask whether I wanted to specify a username & 
password, or just use their default dummies. I chose the dummies -- and 
realized in the night that I've never changed a username before. 

	I think, repeat think, I could hack it with mv and chown, but I 
had enough sense to try a few manuals and duckduckgo searches. Those 
eventually led me to usermod, and I took a look at 'man usermod'. It seems 
to be fairly powerful -- and therefore dangerous as well as apposite.

	So I ask here: are there caveats, gotchas, and/or other entities 
of their ilk that I need be wary of?

-- 
Beartooth Staffwright, Not Quite Clueless Power User
Remember I know little (precious little!) of where up is.