Also, another way to do it:

$ perl -le'
my $string = "JAZZxxJAZZJAZZxxJAZJAZZxxJAZZ";

print $string;

$string = join "JAZZ", grep [ tr//a/c ], split /JAZZ/, $string, -1;

print $string;
'
JAZZxxJAZZJAZZxxJAZJAZZxxJAZZ
JAZZaaJAZZJAZZaaaaaJAZZaaJAZZ
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