Tags And Titles

Hello There,
I wanna Just Add a new tag to all of my postst that i have published before it means

I Wanna Add a Tag To All Of Wp posst That’s poblished

IS This Possible ? If It is Help me 🙂
Any Plugins ? From Databases ? I Don’t Know just give an idea

_________________________________________________________

Other Question : On My Blog page Title IS Download Music
On The Single Title IS : Download Music
Why ? IT should Be The Post Title ! i have changed my theme couple of days ago my old posts is ok but my new posts not working well

Inna – Hot Live @ Brasil < Posts Title
Page Title : Download Music <
My Post Title Not Showing On The Main Title Of Single Page what is the problem