Barca's 4-3-3 with Messi as False 9 is proven to be successful for many seasons, so you can't fix what isn't broken, however ....
As we all know, against some of the real top European teams and defensively organised spoiler teams we could use a Plan B.
I am only FOR moving Messi to #10 IF we are chasing a cup-tie and must score OR we have failed to score in the first hour of play and have the option of a True #9 to come off the bench, that Messi can play off.
Ideally that Striker should be a physical presence with the ability to hold up the ball, linking play with his back to goal, win aerial duels and possess great movement to free-up space for Messi & Co. to exploit. He should be in his mid-thirties and be content to mostly play a cameo role off the bench for the last 20-30 minutes and occasional starter in times of rotation.
Messi doesn't have the work-rate to play a midfield role for the entirety of a match, not unless he is up against such poor opposition in which case it would defeat the object of playing a true CF to begin with.