[1.6.4] Right Click Event to Replace Block

[ZapterX]

I am coding a mod that contains a tool used to replace a minecraft block with a block from the mod on a right click event while holding the item. I don't know what code to use to actually replace the block wile holding the item. Any suggestions?

[ZapterX]

Is there any easy way to do it without updating? I'm asking because I have a modpack at 1.6.4 and alot of mods aren't updated and I would like to add my mod to the pack before releasing it.

[ZapterX]

Could anyone direct me to an instruction page to update my mod from 1.6.4 to 1.7.10?

[ZapterX]

Thanks for everything!