Using Time Machine to hand-pick files to restore

You can use Time Machine to selectively reinstall anything you wish. Use the Time Machine icon and select "Enter Time Machine". Navigate to the file or folder you want to restore and click Restore.

Reinstalling apps that required an installation program to install on your Mac cannot be restored in this manner though. They are likely to require their installer program again, and may fail to work properly if you restore them with Time Machine. Whatever means you used to obtain those programs, use it again. The documents they created can generally be restored with Time Machine though.

... The thought is that there are software conflicts that are causing my system problems.

That sounds reasonable but reinstalling Mountain Lion does not erase other system modifications you may have made. If you or the Apple Store were to erase the system entirely, reinstalling problematic system modifications will result in the same problem. Many apps that predated Lion or Mountain Lion have been known to cause such problems, so research their developers for an update known to be compatible with Mountain Lion.

LQ Guy says

Keeping in mind that the computer will "behave" as though it's brand new when I get it home and plug it in,

You will plug in the hard drive then go to the Time Machine symbol in the menu. Press it to activate the dropdown. Then select browse other Time Machine Backups. Do not set up Time Machine before doing this!

Yes, I think that is an excellent idea. To reinstall your iTunes Library (for example) "Enter Time Machine", and navigate to your Music folder, and select Restore. Same for your iPhoto Library. Both libraries will likely need to be "upgraded" the first time you open those apps after restoring their libraries, so expect that.

Firefox bookmarks can be restored the same way. They are stored in your user Library under

~/Library/Application Support/Firefox

To navigate to that folder directly copy the above line then use the Finder's Go > Go to Folder... selection and paste it in the path field. "Enter Time Machine" and restore the entire folder's contents from your backup. Download and install Mozilla's latest version of Firefox first.

You would be better off creating your printer queues completely anew with Mountain Lion. Sometimes they work properly after upgrading from Snow Leopard, and sometimes they don't. Eliminate all doubt and create new ones.

Hold off on reinstalling MS Office unless you decide you cannot live without it. There are many alternatives available today. Pages will open Word documents, with the caveat that complex formatting does not generally transfer perfectly.

macjack wrote:

LQ Guy says

will Time Machine recognize the new system?

Question is, can TimeMachine just migrate user accounts and nothing else?

How does one stop TM from updating to reflect the new configuration?

Does one need to create a similar user account, and will it be able to cherry pick the desired files from the TM drive?

I'm under the impression TM is too automated and doesn't work well to restore just what one wants to a freshly installed system.

I could find out, but I really don't like it, nor do I want to waste a drive on it when bootable clones are a much superior option.

Most commonly used backup methods

macjack wrote:

It sounds like they're doing a clean install. But... will Time Machine recognize the new system?

Yes. I have done this many times.

The only problem would be related to replacing the logic board, since that is a different Mac as far as TM is concerned, and in that case the only additional step is to "inherit" the old backup.

It will not be necessary in your case: The only problem would be related to replacing the logic board...

Apple is not replacing the logic board.