A creature can have multiple regeneration shields. A regeneration shield isn't an ability, but even if it was, a creature is allowed to have multiple instances of the same ability. For example, Maelstrom Wanderer has two instances of Cascade, and Sublime Archangel can give Exalted to creatures that already have it.
Even if a creature could only have one regeneration shield, it would still be legal to target a creature multiple times with Broken Fall; it just wouldn't do anything useful. The card would need to be worded something like "regenerate target creature that hasn't been targeted by a permanent named Broken Fall this turn" if they wanted to prevent this.
There's no rule that says you can't cast the same card multiple times, if it somehow keeps making its way back to your hand.
There's no rule that says you can't target a creature with an ability if you've already targeted that creature with an ability from that same source. (but even if there was, Broken Fall becomes a new object every time it changes zones, so it wouldn't count as the same source anyway)
There's no rule that says Enchantress' Presence can only trigger once.
So you're good!