Just wondering if having 2 copies of my Houdini and render non-commercial licenses causes any ill effects. I have one apprentice HD license (as it is paid for). Could these multiple licenses ever cause program errors? Thanks.

Installing several non-commercial license keys does not cause any problems. The license server will check out the most appropriate one (version-wise, etc) when Houdini sends a license verification request. Or, if a few licenses are equally appropriate, the license server will pick one at its own discretion.