My suggestions on what to cut:

• I don't think Celestial Dawn is a great include in Sen Triplet decks anymore considering the mana rule change.

• Not sure how good Faith's Reward is, considering you don't have many permanents aside from artifacts, and some of your permanents will be your opponents' (making this card less effective).

• Commandeer costs too much for its effect I think, 7 mana is a lot to hijack someone's spell.

• Debt to the Deathless, not sure what's this doing here. If you need a wincon in Sen Triplets try something else like the [[Sword of the Meek]] + [[Thopter Foundry]] + [[Time Sieve]] or [[Thopter Assembly]] + Time Sieve combo. These two combos will generate infinite turns for you, Debt to the Deathless costs a lot to get running also.

• Paradise Plume, Sol Grail, and Khalni Gem. You could probably get rid of these for the three guild signets usable in your colors instead. They're cheaper and allow you power out Sen Triplet earlier.

• Rupture Spire, kinda slow. Consider running the artifact lands or something else other than this.

• Necromantic Selection, why not run [[Wrath of God]], [[Damnation]] or [[Toxic Deluge]] instead? They're cheaper and generally more effective.

• Indomitable Archangel, [[Leonin Abunas]] is easier to cast and doesn't have metalcraft requirement. Also consider running [[Karmic Justice]] to protect your artifacts.

• Darksteel Forge, kinda slow in my opinion. You could run [[Darksteel Plate]] if you really need to protect Sen Triplets.

• Debt of Loyalty, not sure how often this works in your playgroup, but it seems kind of situational to me (especially with exile-based removal).

• Memory Plunder, you already have two cards that already do this on a greater scale. Not sure if you need another.

Lastly, consider running [[Sun Titan]] and [[Clever Impersonator]].