Frankly, if I was Zeke...
-ACTUALLY TREAT YOUR BROTHER NICELY. Don't rope his ass into a genocide plan immediately after meeting him. Actually do family stuff, bond with the nigga, don't just go beta tier Gendo on him. This might actually make him less receptive to the Rumbling if I played my cards right.
-Distance your ass away from the wall breaching as much as possible, reflect all blame on Reiner and Bertolt, as much as it would suck to do those two dirty. Do so in a sneaky way that the two won't catch onto however; don't need Eren finding out I backstabbed two folks for an incoming plan.
-Once reunited with Eren, slowly but surely do some things to destabilize the Marleyan military complex. Fuck up some factories, do some hit and runs on training grounds, blow away government officials that trust me. DO NOT LET GABI OR THE WARRIORS FIGURE OUT IT'S ME AND THE SCOUTS: otherwise this shit goes downhill fast.
-The Tyber speech plan will go as canon, but with a key difference; I eat the warhammer titan. With my combined monke skills and the warhammer's abilities to create weapons of any sort, I will become a long ranged death machine. Pieck gon' get sniped lol. Also kill Gabi in a "coincidental accident", I don't need my brother getting sniped at the worst moment possible. Also to save Sasha, Niccolo doesn't need his waifu stolen so cruelly.
-When Reiner inevitably leads the counterattack, BLOW AWAY THE FUCKING AIRSHIPS BEFORE THEY DROP TROOPS. Last thing we need is ground forces complicating stuff for the Ymir connection. Get those retarded Yeagerists to finish anybody that survives the crash.
-Once connected, get Eren to agree to turn all Eldians tired of the Marleyan rule into superhuman warriors that will liberate the populace from tyranny; Not titans, but smaller, human shaped fighters that will be on par with the Scouts in terms of killing skill. They will retain a certain amount of personal control, but to make sure we don't have some cucks in the Not-Tyrants dull all senses of regret, remorse or hesitance. EVERY Marleyan government official, soldier and politician will be terminated.
-If Eren still tries to do the Rumbling as canon, talk-no-jutsu his ass into believing that the future is never set in stone, and that taking his visions as total fact is locking himself away from options he might have never thought of. If he still persists, reset his memories lol, I'm God.
-With the aquisition of the Founder complete, Instant Transmission the remaining Eldian populace to safe locations, as to lessen Eldian casualities for what's to come next.
-Activate the Rumbling, but use it in a specific way. March a certain amount towards Marley, and trample the fucking place into the ground. Then, transport some Eldians to the newly vacant Marley land, and initiate colonization.
-Use PATHs to spread a message; the Eldian populace will be left alone, and in return the other countries will be left alone. Bloodshed will only occur if action is taken against Eldia and its new colony. Eldia will have no plans of further conquest, the beef was all against Marley and its cruelty and historical revisionism.
-Turn all Eldians that were titanized into humans again. Then resurrect the fallen, since if it happened to Zeke in canon it can happen here, I'm God for fucks sake. Get Historia back with Ymir again, those two went through some shit and I ain't having no NTR bullshit with the queen. They deserve some happiness after all the bullshit that preceded it.
-Kick back and chillax with Eren and pals, having killed off only the real aggressors of the problem and given Eldia new land to live in, plus given the world a fair warning. If they try some shit, do what I did with Marley, but lessen the chaos of it; only target government locals and industrial sectors.
-Finally, convince Mikasa to stop being a fucking hesitant bitch with Eren and just fucking ask him out on a date. Just up front, tell his ass she wants to go for some food or some shit, I don't need my brother to get all Eliot Roger on me just when I fixed everything.
And that, is how you save Eldia, stop any potential counterattacks, and get people to stop acting angsty about who's fuckin' who. There, no need for foot fetishing the whole planet lol.