Discriminating analyzers whitelist and blacklists.Contact admin about alias/username on whitelists

...These are around about ways to do what you're asking.  

1. You can search for posts by an alias just like you can search for posts by a certain handle.  

Click the search button on any board, enter the authors name (the alias you're curious about) change the number of days to 3000 (or however many days TER has been in existence if you want to do the math) and click search. You'll get all the posts by that alias on that board. This would give you some idea of how long the alias has been in use. You'd have to do this for every board to be sure you found the first post.

2. You can use the above method to see if a PM's author is an alias.

If the PM has a subject line which is from a post you made that will give you which board to do this on. Go to that board click the search button. Enter the PM author's name into the author field of the search. Change the number of days to 300 or whatever just to enhance your chances of getting a hit. Click search. Then open any post that comes up. Look at the posters name. If it's in teal it's a regular TER handle. If it's in black type it's an alias.

If the PM has a subject that isn't from a discussion board post you could still do this but you might have to check several boards before you get a hit.

3.  Is it possible for a reviewer to change his/her username to his/her alias-name, and merge the two sets of reviews and Whitelists?

I don't know but I would think TER admin could do it if they were asked to and they deemed the request was for a legitimate reason. Asking them would be your best bet on getting this answered.