I believe the rules on the NBA side did not change under the new CBA that was signed in December.
The NCAA however put some more restrictions requiring that the possible early entrant formally withdraw by no later then May 8th. And also the NBA allows that player to withdraw twice, however the NCAA does not. The NCAA only allows that player to do it once and still keep his eligiblity:
"Early entry" Players who are not automatically eligible, but wish to be drafted, must declare their eligibility no later than 60 days before the draft.[12] After this date, "early entry" players may attend NBA pre-draft camps and individual team workouts to show off their skills and obtain feedback regarding their draft positions. Under the CBA, a player may withdraw his name from consideration from the draft at any time before the final declaration date, which is 10 days before the draft.[13]
However, the NCAA adopted a rule that took effect in August 2009 that requires players at its member institutions to withdraw no later than May 8 to retain their college eligibility; the first draft affected by this rule was the 2010 draft.[14] A player who declares for the draft will lose his college eligibility, even if he is not drafted, if any of the following is true:
The player signs with an agent.[15]
The player has declared for and withdrawn from a previous draft.
Although the NBA collective bargaining agreement allows a player to withdraw twice,[13] the NCAA only allows a player to enter the draft once without losing eligibility.[14]
http://en.wikipedia.org/wiki/Eligibility_for_the_NBA_Draft