I'm not sure I quite understand what you were want, but hopefully I can help a little.
By default the system random expressions use the browsers inbuilt PRNG, which uses a random seed ( the seed is unknown to the consumer, and cannot be set ).
The AdvancedRandom plugin has its own PRNG, separate to the browsers one. It uses this PRNG as a source of randomness for all its expressions. This PRNG has its seed set when your game starts. If the user specifies a seed in the object properties then it uses that, otherwise it will use the browser PRNG to generate a unique one. During runtime this seed can be read, and changed. It's also possible to generate new unique seeds from the browser PRNG using the
There's no direct way to get a value from the PRNG in Advanced Random. But as Fib says there is a check box in the Advanced Random properties which changes the PRNG that the system random expressions uses to be the one in Advanced Random. Allowing you access to those random expressions as well.
So in summary, the PRNG is only predictable if you set the seed to be a predictable one and you can create a new unpredictable seed at any time.