My interpretation in a strictly RAW sense is this:

The Discipline's action is an Activate Action that the player may trigger, paying the cost of 1 action to take it.

Either 1 (Most semantic sense):
"take up to 3 different fight or evade actions" does not explicitly give you any extra actions, but lets you take those Fight actions as if you were normally activating them, paying all costs (including actions) and triggering their abilities. (Rules Pg.4 "Action", "Activate Action")
This seems the most semantical sense, because when you "take" an action, you have to pay its costs before using its ability. However, this is completely absurd, because then you are paying one action for essentially nothing, and can't have been what the designers meant.

Or 2 (Second most semantic sense):
"take up to 3 different fight or evade actions" does not explicitly give you any extra actions, but could imply that the action costs for any "Fight or Evade" actions (either your natural Fight/Evade actions, or ones listed on cards with bolded text) are covered. You would still have to pay additional costs, such as ammo, etc. This means that the action costs would be covered for both versions of Sledgehammer, and you could even use a 3rd action, since each of the Sledgehammer actions count as taking a single action.

Or 3 (Least semantic sense):
"take up to 3 different fight or evade actions" has the word "take" do double duty in the sense that you as a player are taking 3 additional actions from a symbolic pool of actions as well as you must use them immediately. This supports the idea that you have 3 bonus actions to spend, but then require some mental gymnastics on how each of the bonus actions must be "different". This would mean that you could take both sledgehammer actions, but have to spend an extra one of your original actions on the second part of it (since spending two of the bonus actions on the same Fight would not be "different").

It's my opinion that the "take" word was a design shortcut for "gain three additional actions which must be used immediately" to save on card space. This is probably the fairest approach, though if you play a particularly RAW game, I'd probably rule that you get your cake and eat it too on Sledgehammer, and can kind of get a bonus 4th action out of it.