From what I´ve heard. Agassi has been playing with the same racket for the past 7 or 8 years.
Just paintjobs, same as Safin, he is still playing with the Great Head Prestige Classic.
Concerning Agassi, not from Us Open 2003 'til Roland Garros 2004, he played with 3 different Liquidmetal look-alike. From Queen's 2003, he played again with his old beam.
Neither during clay season in 98 (he used a Head painted racket that looked like his old Prince), then he used a string pattern of 20 x 21 until Rome 99. Since then, it's a 18 x 19 (like the model sold on the markets).
About Safin, he played a little while with a Dunlop 200G, but unsatisfied he painted a Prestige Classic which he's always used.