I had something similar where I wanted to expand the last thing added.
You can use toc.expandItem(toc.dataProvider.source,true,true,true,null); where in your case the toc.dataProvider.source part would be the item you want to expand.
The real trick for me was that after using toc.expandItem make sure to run toc.validateNow(); or nothing will happen.
I thought there is a toc.collapseall or something like that but I can not find it. I found in mine that when something is added it collapses all of them anyways. The command toc.validateNow(); could make that happen.
If you have a link to the item (the toc.dataProvider.source) above you can also change its font I think. There is code in there that changes the font for scale dependencies so maybe look for that. Check TocMapLayerItem.mxml.
Hope that helps.