How can you install rear ac in Mazda mpv lx 2005 that you bought recently is this something that can be done easily or difficult or risky?

This is not something that any home mechanic nor even a Mazda dealer/mechanic would or should attempt. It would require a major interior ripout, plumbing of A/C lines, wiring, installation of vents, controls, condenser, etc. If you didn't buy the van with rear A/C it's too late. Sorry, Your Humble Home Mechanic. P.S. Anything can be done if you throw enough money at it and I have a feeling this would require a lot of throwing and give you a sub-standard system plus with the extra incentive of creating new rattles!