It used to be, but with the website update they removed this feature. The only thing that is possible now, is to "change" the e-mail. If you do not wish to have it set to your e-mail, then just change it to a random, fake e-mail (although this can cause major problems if you are trying to recover the account, as they send e-mail to that address). If you are trying to sell the account, simply change it to the buyer's e-mail address after they have paid for the account. It takes 2 minutes to do, and once that is done then you cannot play around with it anymore and it secures it in their posession.
Lately I've noticed it's taken a couple hours for Jagex to send me the authorization codes I usually offer to go first so the buyer feels more comfortable. Besides, even if they try to scam you, since the account is yours (I'm assuming) you can easily recover it.
An alternative to both of these is to make a new email account, register the Runescape account to the new email, and then sell both of these to the buyer.
