In my ARM based custom board, I flash u-boot to NAND whenever I do changes on that. (putting some debug statements/modification). Is there any way to directly load the uboot ima
The problem here is that what you are trying to do goes against the philosophy of what a bootloader is. Most processors require that code starts from Flash. That code is called a bootloader. That is what U-boot is.
However, if you want to modify U-boot so that it is not a true bootloader, then you can do whatever you want. It's just software. But don't expect any mainline support for the above reasons.