First of all thank you everybody for the comprehensive answers.

Then, let me agree with MCantu about the problems created by the 4tpy script, that allows to make the conquest of great extensions of land in very few years (from 25 to 35). That really doesn't seem historical, while with the 2tpy system everithing is far more realistic.
Please explain me also what black and grey Death are.

Last but not least let me ask two more questions!
1) Does the elimination of the 4tpy script affect the functions of the mod or will it run without problems?
2) Does the activation of the script prevent the slave armies to move from the cities where they are statione once the original named characters present in the descr_strat.txt are dead?

Thanx again!