Manipulating Search results

In the old iTunes I was able to search my music (1000's of songs), for specific words. I'll use 'christmas' as my example. the results would show and I could highlight the whole list of results and change the info, example, change genre to 'christmas'. this is how I created my playlists. with music, I can still search, but can not highlight them all to do a mass change. is there a way? or do I now need a third party app to do what I used to do in iTunes? please help, my playlists are a mess!