My 2001 LS430 has a dead battery with the red "change battery" light on. Any special percautions needed to get the old battery out and a new one in? Will this mess up the ECU?

 

That usually comes on when your alternator is having issues. Or Battery is not charging. When does the light come on? while driving? and does it stay on for the entire day?

Not special procedure for the battery, and nothing that would harm the ECU... even if you connect it the wrong way, the worse that could happen is a dead fuse.

 

Seems like the battery should be replaced.

Using a 10mm box wrench, disconnect the battery negitive lead first, then the positive.
The same wrench is used to remove the outer single bolt on the hold down bracket.

Reinstall in reverse order, installing the battery ground last, after checking the remounting and polarity.