PRNG - Algorithm: Performance vs Readability
There is no one answer.

Performance

How often is generate_normal called? Is it called on a program critical path or only during set up? 

Could you cache a bunch of numbers before hand and only replenish the cache when you run out?

Readability

How many people will read this code over its lifetime? How often will you have to come back to the code?

Compromise

If you notice a substantial penalty using the private const construct, then do the following:

/**The Multiplier. Suggested 1993 by Park and Miller.*/
private const MULTIPLIER:int = 48271; // folded into code below

/**The Modulus. Suggested 1988 by Stephen K. Park and Keith W. Miller.*/
private const MODULUS:int = 2147483647; // folded into code below

...

public function generate_normal(total:int):int
{
    // Values folded from definitions ...
    // _seed = (_seed * MULTIPLIER) % MODULUS;
    _seed = (_seed * 48271) % 2147483647;
    // return (_seed * total / MODULUS);
    return (_seed * total / 2147483647);
}