Does installation of CustomRom chage the partition I have some basic question abt customROM

1.When you install customROM, does it change/recreate the partitions in previous ROM   stockROM/Custom) or it just installs the ROM in the  existing partitions (like windows) 

2.What is ROMSlot, is it someting like MBR in windows ? 

3.Is there any customROM that will unlock the bootloader for me and install itself. 

4.Does cynogenMod works in ANY DEVICE  (i.e. Chinese )
No, flashing ROM will not change your partition table. 
No, flashing ROM won't unlock your bootloader (I think that you'll, in fact, need to be using unlocked bootloader to flash a ROM) 
CyanogenMod is made for each device separately. If it's available for your device, you can install it. Go to their website to see if there's an official or unofficial port of CyanogenMod for your device.