Sorry for the extremely late reply and thank you
@Snapsy for thinking of me. But alas i don't use a pump and can't give any pointers on that mater.
I don't deadlift anymore neither (hernia's) so can't even give any advice on that one and my competition days are over. However i can say that when i'm in doubt i try to figure what would give me the worst lifts for the day. In your case that'll be between irregular BS or not wearing a belt. I squatted triple my bodyweight without a belt (old man's voice: "back in my days"
) so it's possible to lift big without one. Did train my core a lot to be able to do this, belts made me nauseous during summer time so dropped them a lot. But the extra stability and having something to push against is nice especially on a deadlift.
Don't know how many people will be competing but i know the time between lifts can be long and if you're going for 3 attempts (i wish you a fourth if that one is still in the rules
) you can go a decent time without a pump which in case of the pump doesn't seem like a great idea especially since your last lift will be the heaviest. On the other hand competition days were always off BS wise, the adrenaline, exercise, ... it can mess you up a bit.
You might want to consider a dry run in the sense that you mimic a competition day and just do 3 lifts in a 30 minute period without your pump and see how it effects you. Or try if you can comfortably reach your desired deadlift weight without a belt (or maybe the first 2 attempts without one).
Above all have fun man, it's good to know there are diabetic competitive powerlifters out there. Wish you the best of luck.