If i install a cyanogenmod custom rom with all the risky complicated procedure on bootloader and next upadte of cyanogenmod comes out with android l so should i have to again go though bootloader and install it or can i install it simply on going to setting upadte update and android update without going to bootloader.
The unlocking the bootloader and installing a custom recovery is a one time procedure, for future updates you just need to flash the zip file and you are good to go. Having said that, since you feel it is a risky complicated procedure, in case you have a phone that is mentioned on this Page then the whole process becomes a lot more simpler and opaque to you! At the end you will have a phone with the last stable release of CM for your phone, what this also does is take care of the messy steps, so if you are unable to root your phone just using CM Installer will unlock a whole new world.
Nope unlock bootloader and installing CWM is one time (unless you want to update the Recovery) Update or install Zip file it via Custom Recovery