ESN swaps are considered a bad thing to discuss on forums so my answer is a bit generic.
You can revert the Evo settings if you have the info to put back, however, expect a LOT of reading, troubleshooting, headaches and labor to swap over a phone. Also, by the time you are done with it, the Evo will be nearly worthless so I wouldn't worry about it. If you even want to consider this, you should probably read a lot about all of it, including pros and cons and then see if you can even get the info you need from the OV. If you can't manage that part, you may as well give up before you buy the Evo.
My advice to anyone even considering it at this point is simply don't.
If you have any sort of a job, at this point you are better off waiting for the the 3D or One V and not having to deal with the troubles this brings with the whole thing and future troubles you may encounter (such as laws changing, terms of service crackdowns, etc...).