Stacking modifiers

I'm considering playing a bladesinger wizard in an upcoming campaign. I noticed something, and I'm not sure of how this works so I'm asking here.

One of the benefits of a Bladesong says:

Focus. When you make a Constitution saving throw to maintain Concentration, you can add your Intelligence modifier to the total.

One of the new feats in Arcana Unleashed, the Conjuration Adept says:

Persistent Conjuration. While maintaining Concentration on a spell from the Conjuration school, you gain a bonus to Constitution saving throws to maintain this Concentration. This bonus is equal to the ability modifier of the score increased by this feat.

Of course, I would add +1 to Intelligence if I take that feat.

So, does this mean if I cast a Conjuration spell, and I have to make a save to maintain concentration, while Bladesong is active, I get to add my Intelligence modifier TWICE?? They are two different features. So, do they stack?

Yep, they'd stack as they use different wording. One says you can add your Intelligence modifier and the other says you gain a bonus equal to your Intelligence modifier. 

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Modifiers can stack, effects can't. The only modifier that is explicitly disallowed to stack is the Proficiency Bonus.
All other modifiers can stack so long as they don't come from the same effect.

Quote from Davyd >>

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Is there an actual rule that says this anywhere?

There's a rule that says this about your proficiency bonus, but I don't think there's one that says it about ability modifiers.