RealGM

Can a player such as Lance Stephenson - released/waived/contract expired - after March 1st sign onto another team to finish out the regular season? Am I correct in thinking he would not be eligible to be on the playoff roster if his new team qualified?

1 Any player not on a roster can sign with any team until the season ends.
2 Such a signed player is playoff eligible if he was not waived by another team after Mar 1. So the answer to your question is "it depends on how and when he became a free agent."

Yes Stephenson can sign and be eligible for the playoffs. This is because he was on a 10 Day Contract. Works slightly different for 10 Day Contracts. He was not waived. His contract simply expired.