Fear not my friends!
This is a very simple guide that will teach you on how to get to your realmlist and change it whenever 3.0.2 is released for private servers!
Simply go as you would to your normally change your realmlist:
My Computer >
Local Disk C: >
Program Files >
World of Warcraft >
Data >
enUS (or enEU depending on where your from :P)
Realmlist.wtf
And bam it's as simple as that.
Your realmlist should look a little different than before you updated
Code:
set realmlist us.logon.worldofwarcraft.com
set patchlist us.version.worldofwarcraft.com
set portal us
Don't mess with the set portal part.
Changing your realmlist when 3.0.2 private servers come out SHOULD be the same, but considering it hasn't come out yet I cannot tell you that for sure. 
*I posted this guide for players who are worried about where their realmlist is so flaming isn't appreciated here. I have seen a few people from different sites wondering where the realmlist is.