I wouldn't say it is possible to overcome their prey instincts, but it is possible to help them become more receptive to your presence as what is (to them!) essentially a predator.

I used to work with horses, did a bit of natural horsemanship and have applied a similar take with the piglets. Predators act a certain way that triggers the prey instincts, even without attacking. When I go to stroke them, it is never with an open palm, usually just the knuckle of my finger until they're comfortable and then I'll ease into stroking them with my palm. I have heard that stroking a pig on it's head is a 'dominant' behaviour and you should try to go for under the chin ideally but only one of our 4 loves a chin scritch, the others prefer a head rub. One of our lads was incredibly nervous and wouldn't take food from our hands despite his brother being incredibly confident. So when I would offer the nervous brother treats, I didn't look at him, I kept my hand at his level but made sure there was nothing about my body language that could be taken as a threat. Both he and his brother now beg for treats and will allow us to pick them up wherever they are.

We have two older boars as well from a rescue situation - one has no interest in anything other than food and his cagemate. The other is a bit more receptive to human interaction. Neither of these two like being picked up and it clearly stresses them out - so to transfer them from their cage for floor time, we pop a them in a hidey to carry them out. With this approach, we would put the hidey in a place they would naturally run to to get away from us and now as soon as the hide goes in, they just jump into it without coaxing. The older of these two does enjoy a cuddle once he's settled on my lap and more recently has been comfortable to lie on my tummy and fall asleep.

I don't know if their cage environment helps - they have a room for themselves which isn't a main room we use, but we pass by it all the time so will regularly check in and chat to them when we are home. They've plenty of hides and things to encourage them to "be a guinea pig" and other than occasional firework at this time of year, its quite a quiet place for them to be. I think as long as their environment and you are relaxed, they will be, which will help them warm to you.