<p>Possibly, but still a risky strategy.</p>
<p>There is a definite downside to reneging on an ED acceptance to Oberlin, namely running the risk that there will be no later offers that are more affordable or that any subsequent offers made in good faith might be rescinded. Increasing the probability of acceptance by applying ED to Oberlin only matters if you wind up attending Oberlin, in which case the existence of other offers is moot. I rather doubt that you will get a better FA offer out of Oberlin by producing a copy of the RD offer from a competitor, thus proving that you did not withdraw your other applications as promised. If there is another school out there that wants you more than Oberlin, an ED application to Oberlin may not disqualify you in their eyes but it is not going to make them think any better of you. If their offer is still on the table after they find out about the Oberlin ED acceptance, it would have been there anyway had you not applied ED to Oberlin. It seems to me that you have nothing to gain and much to lose in this situation.</p>