It's up to you really.
Note that if you had actually erased the current image and just added the new one to flash then you would not need to have changed the configuration register as that would have been the only image and so it would have booted that one.
However most people, including me, don't do that just in case there is a problem with the new image. If you have multiple images in flash and you want to choose one that is not first in the list then you need to modify the configuration register and the boot variable to tell it to use that one.
When i was doing a lot of 6500 upgrades i would simply change the boot variable to include both images but make sure the image i wanted to boot was the first in the boot variable string. Also worth bearing in mind that sometimes you have an image in onboard flash and one on a compact flash card so again if you wanted to boot the compact flash image you would need to modify the boot variable.
It really comes down to what you want to do ie. now you have booted the correct image and verfied that it is working you could if you needed the space remove the old one and reset the configuration register back to what it was.
The advantage of using 0x2101 is that as long as there is an image in flash it will always be able to boot.
The advantage of using 0x2102 is you can have multiple images and choose which one you want to boot at anyone time, including when the image may be on a flash card.
Usually i used the boot variable to decide which image to boot and did not rely on the order in flash.
Jon
