If you enable 9.999.999 money for example and save the game this value will be saved in most cases.
This can differ from code to code since a specific value be found at many places in ram. Sometimes the cheat will only show the 9.999.999 but it won't be saved.
A cheat can kill your save game if the master/enable code is not the proper one for your version of the game.
PS2 SCPH-70004 V12 PAL + HDCOMBO + 160 GB Samsung HDD + OPL 0.9.1
PS2 SCPH-70004a V13 PAL Satin Silver
2 x Official Sony 8mb card +FMCB 1.8c + uLE 4.42b
Datel Max Memory 32mb card +FMCB 1.8b + uLE 4.42
Memor32 + Memento FW 1.2e