The artist formerly known as provocative may have nixed his saucier material, but the man behind ''Erotic City'' can still stir up controversy. Thanks to the crafty strategy of including a copy of his don't-call-it-a-comeback album ''Musicology'' in the ticket price for his current tour, Prince is sitting near the top of the Billboard chart. ''Prince is ahead of his time and thinks outside the box,'' says Randy Phillips, the tour's promoter, of the ''Musicology'' scheme. But record labels cried foul, complaining that the CD-concert combo sets an unfair precedent in tallying sales. Now Billboard's announced an amended policy that stipulates ''the consumer must be given the option to purchase a CD with a concert ticket for [the sale] to count toward the chart,'' says Billboard chart director Geoff Mayfield. However, ''Musicology,'' which has moved 800,000 units since its April 20 release, has been grandfathered out of that rule. With 1.5 million fans expected to see Prince this year, he'll likely have a spot in the top 20 for months. Almost 2 good 2 B true.