I understand the restrictions placed on future season payroll when it comes to making trades, so I'll get right into it.

I didn't realize I was so close to my threshold and agreed to a trade with another owner. It's a 3 for 1, where I'm getting the 1 back- a solid SuA guy that was only signed through the end of this season (we're close to trade deadline). I asked said owner to re-sign the player for the 3 years he was asking for. Said owner did this, re-proposed the trade and I accepted. However, I'm now about a million over my future season budget.

My question is this:

Our trade will get nullified tomorrow during the 3 pm cycle (when it was accepted today), correct? What if I agree to a trade during the cycle after our trade was accepted that clears money for me? Essentially our trade deadline is during PM2 tomorrow night, so I'd have to agree to a money dump by around 7 tonight to be able to re-submit my trade and get it through before the deadline?

You need to agree to a trade that will reduce your budget in time for it to clear a half-cycle before the re-proposed trade clears-- this means, I think, that you have until about 7 PM tomorrow, not today, to get that trade offered and accepted.

So no matter when I agree to another trade, the first one will get processed before it, thus will definitely be nullified?

I'm close on a deal to clear the space- so I guess my plan of action will be to get that one accepted by the end of the 7pm cycle tonight, the real trade will be nullfied tomorrow during the 3pm and then i should resubmit the real trade when the 2nd is processed during the 7pm cycle tomorrow?

You'll want to have the trade resubmitted just a 1/2 cycle after the other trade gets accepted. 

Since you KNOW the original trade will be nullified, you can re do it even BEFORE the original is nullified if you simply add $1 so it is a "different" trade than the one already pending that will be nullified.

Perfect. Just had my salary dump accepted at 2:00, my original nullified at 3:27 and the original re-accepted at 4:01. Hopefully, if all goes according to plan, salary dump gets processed tomorrow between 3-4 and the original gets processed between 7-8.