I am currently on stock 2.1 eclair and I was thinking about upgrading to 2.2.1 froyo using the update.zip file and I wanted to know how would I be able to downgrade back to eclair if I was not satisfied with froyo. Thank you in advance.
Yes, you would be able to go back to stock after update. Just look for youtube videos for visual explanations. They're pretty good.
When ever I go to youtube I find videos of how to upgrade the epic. But when I look to downgrade I find videos of how to downgrade the captive and not the epic. Would it be the same steps and files?
Just like you need the file to install 2.2 you would need the 2.1 file to install. The procedure is basically the same for either one.
There is a good write up on how to flash with Odin here.
Scrool down to "Odin Stock Flashing "
It is possible, I'm not sure. But this might help:
Just read the whole thing carefully.
As far as I know, So long as you use the stock SPH-D700-DI18-8Gb-REL.tar.md5 file you will be back to stock 2.1