Is it possible to wipe out iMac with ML upgrade and THEN reinstall SL from disk, back up with TM?

Question

Iv'e been going round and round with my iMac ever since Genius bar employees "upgraded" me to ML while replacing Seagate HD per the recall. THis is a late 2009 27-inch iMac that came with SL.
What I think might solve this once and for all is to completely wipe out the hard drive and THEN reinstall SL from the disk that was shipped to me by Apple.
Here's what has happened thus far:
1. iMac was working fine, but per emails from Apple, replacing the Seagate HD that came with the computer was advised. Made appt, took it in after backing up to external hard drive.
2. Picked up  the iMac first week of August. Found that they had upgraded me to ML.
3. Proceeded to put back contents of backup from July 27 (before the hard drive was replaced, all saved in SL).
4. Immediately after back up was reinstalled, realized that iPhoto contents (ALL of my saved files/photos, movies, etc, both work and personal) are inaccessible. Also, fan will not stop running (and this is true even when there is no user signed in, ie, no CPU-intensive programs running). Programs that worked in SL no longer work with ML (iWeb, etc).
5. Have been in  contact with Apple numerous times, and finally got a senior tech to work with me via phone. I had a SL disk borrowed from a friend (the 27-inch was a replacement for original iMac that was defective and never received any install disks with new iMac Jan 2010). Per instructions from Apple tech, backed up iMac, then tried to reinstall with SL disk. When the progress wheel only kept spinning, he said that the disk I was using must be incompatible and I waited for a replacement SL install disk to be mailed to me.
6. Called back when I got the new SL disk, and then we tried it again. When the progress did the same thing, ie just spinning, Apple tech said that I must have a hardware problem and he instructed me to make another appoitment with the Genius bar. I did that and am supposed to take it in tonight.
7. Apple tech said it  must be a hardware problem, that the super drive would not read the install disk, BUT, the super drive (actually both of them, one inside the machine, one external super drive  purchased separately) has no problems reading audio CDs. It is ONLY the SL reinstall disk.
That, along with the continually running fans that have also been deemed by Apple tech to be bad hardware (which were both fine before the upgrade to ML) make me think that it is the ML software that does not work properly with this late 2009  iMac. It was designed for SL, not  ML.
I suspect that if the hard drive on the iMac is completely wiped clean and SL then reinstalled with the disk that was mailed to me, this would put my machine back in order with SL as the OS.
I'd like to try that BEFORE I take this iMac back to the Apple Store. I have the back up from July (before ML was put on as the OS) and that's what I'd like to put back on. I can more easily save  jpegs that were savde after ML was put on as the OS than I can save everything (one by one) that was on this iMac from Jan 2010 till July 2013.
Is there anyone who can give me a yes or no, whether this would work or not? Wipe it all out, start fresh with a new SL installation and back up from that July 2013 backup?

Answer 1

Yes it is. That is why you got a set of reinstal disc with your Mac. For just this purpose.
But if you have a 2009 model it might of come with Leopard. But you should still be able to use that reinstall disc or the retain Snow Leopard DVD you used to upgrade to SL to restore your Mac from a Time Machine backup.
First you need to boot the system from either the original reinstall DVD or the retail SL DVD and use Disk Utility to Repartition the drive as One Partition. you MUST do that to get rid of the Mt Lion Recovery HD partition. Once that is done there should be an option to Restaore your Mac from a TM backup. Have the backup drive connected before you start the system from the Reinstall DVD, either of them whichever you chose.