You can both extract the number and replace with the new ones, as given in the following snippet;

# assuming; ...
my $str = "WB(1,2)=    0.000, 1.23, TB(1,2)=     0.0,  253.0, TMB(1,2)
+=  0.0, 1.0,  SL(1,2)= 0.00, 1.00";

sub replace {
    my ($extracted_number) = @_;

    # calculate or query the new number. For example;
    my $new_number = $extracted_number + 1;

    return $new_number;
}

$str =~ s/
    (?<=,)            # Precondition: There should be a comma before,
    \s*
    (\d+\.\d+)        # ... and it should be a floating number!
/replace($1)/xges;

print "$str\n";
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