s[ 
    ( 		## Capture
        \(      ## from an open paren
        [^)]+   ## all non-close paren chars
        \)      ## upto the close paren
    ) 
][ 
    ## assign the captured text 
    ## to a local variable so that it can be edited
    ## and then replace all ,s with ;s
    ( my $x = $1 ) =~ tr[,][;];
    ## and return the modified text to replace that captured.
    $x 
]
g  ## globally
e  ## execute the replace as code 
x; ## extended notation to allow whitespace and comments