This thesis focuses on a detailed implementation of the Relative Cyclic Component Mode Synthesis (RCCMS) approach on cyclically symmetrical systems with an in depth development of the algebra involved. Subsequently, it is showed how stiffness and density mistuning can be efficiently introduced in the final Reduced Order Models (ROMs). Eventually, numerical simulations are presented to reveal the accuracy of the RCCMS approach in predicting natural frequencies, modeshapes and linear forced response of the reduced systems of a bladed disk. In conclusion, the performances of the systems built with the two types of mistuning introduced are compared to show how, in some cases, density mistuning can be a valid alternative to stiffness mistuning.