72-year-old musician will release the song next Tuesday, ahead of the July 4 holiday.
The Mayor made the decision after consulting with victims and family members.
She made a surprise phone call on Monday.
Only 20 percent of victims have applied for compensation.
They say they have more determination to run after the tragedy.
Runners unite the world after the Boston Marathon tragedy.
Thus far, $28 million has been raised for the charity.
The Boston Marathon was halted two weeks ago when two bombs exploded near the finish line.
Security is top priority for the World Championships in August.
Fifty-thousand bracelets will be distributed to participants of this year's race.