There was another post about this recently and the answer is that you definitely can remove the no expiration option and add more days or other options to the ticket. As the others have said, you need to wind up with a more expensive ticket in the end, so you can't just remove the no expiration option, but since it's not terribly expensive for a 2 day ticket this should be a problem.
Do use the ticket first, to bring it up to current gate value (removing no expiration from a used ticket is no problem because you don't use the no expiration option until the 15th day, and by then it's not changable anyway).
At that point you'll have a ticket that is worth $185.31 (including tax). You could upgrade it to pretty much any ticket you want because everything else will be more expensive.
Removing no expiration from a ticket with a lot of days may be impossible, especially if you already have the park hopper or water park options on the ticket because it might not be possible to come up with a combination that would be more expensive than the original ticket, but in this case the OP will have no problems.