I have been building around and needed a SAFE receiver for the beginners in my club, and I was wondering if I could buy an AR636B and program it with SAFE
It would probably be much easier and cheaper to use something like the FT Aura 5 lite than the HH AR636B. Especially if you do not already have the Horizon Hobby programming cables.
If already using Spektrum much easier to use the AS3X receivers, the only thing you have to watch for is some are locked depends on which plane they came out of. Spektrum has a good set of videos on how to reprogram the AS3X receivers on there website. This link shows the planes that have reprogrammable receivers in them.
The Hobby Eagle stabilizer is another option, it has the exact same functionality as SAFE. It will work with any brand of Rx. Several versions to chose from, just pick the one with the features you want.