Resolving or undoing Migration Assistant / Time Machine Back-ups?

Can I undo a Migration Assistant process by using Time Machine to a date before it was preformed?

Here's what I did & the related info of the 2 Mac's used & what I was 'hoping" was going to be the result & reason for using MA:

My fathers iMac G5 ((PowerPC- [a complete Apple Fail in my opinion] )) has been having major issues(who's hasn't) lately & got to the point where it would;

1) power on

2) make the Mac tone sound

3) show Apple Logo gray screen

4) show 'Mac OS X' screen with blue process time bar with 'Starting Mac OS X' under the blue bar

5) the blue bar starts to fill in until it looks full & is still in motion(animation) but does not advance from there(system freezes but blue bar is still in motion), until it seems to sleep or hibernate after 2-3min when Screen goes black, the white power light pulses in front, but connected wireless keyboard & mouse clicking do not wake it up. Fans can also be heard running. The only function that seems to work is turning it off by pressing & holding Main Power button for several seconds.

So I wanted to retrieve his files etc off his iMac G5 if possible to my MBP 13" 2011 which is currently running Snow Leopard 10.6

I ran MA app & it made the connection & asked to proceed & what files I wanted to transfer (chose all that were suggested/check marked).

Process took about 2hrs & seemed to run without any issues. But now my MBP computer name was changed to the name of his iMac G5. It either never asked if I wanted it to change the name or if it did I didn't understand what it meant & proceeded with hopes that it was just necessary to run MA, but I do not remember doing that, but admit it's not uncommon for me to forget actions performed when doing computer related processes.

I have not done anything to try & correct or reverse this Migration in hopes to avoid making situation worse but I did hook up my External Hard Drive I use for Time Machine back-ups & noticed when I choose 'Open Time Machine' that my computer's name (Darth Vader's Stealth Fighter) is now my father's computer name (D Chuggers iMac G5) no matter how far back I go in the timeline. And the 'Restore' button on bottom right is inop & not selectable.

So can I or can't I restore my entire MBP to an earlier date as if I never performed the migration? Any help would be 100% appreciated. Thank you.