I expect most uses of Strong manipulation will be the obvious: mess with the strength / range over a given area to induce fusion / fission / transmutation, or extra heavy elements as others have mentioned. However, it might be interesting to look at the level of Quarks and Gluons for weird extra possibilities. For example, the Rho meson is basically a super Pion that almost immediately decays via the Strong force. What happens if you can set up an AoE that supercharges Pions, then prevents the resulting Rho'ons from decaying in the standard way? My guess is that this is an overly complicated and energy-intensive means of getting more unnatural isotopes, as the Rho'ons reek havoc on nuclei in their paths.
Quarks can't seem to exist in isolation. We can't separate them from baryons or mesons, because the energy required is sufficient to create a new Quark, which bonds with the one we were freeing. But if you can somehow block or reduce the Strong force to a great enough degree, could you dissolve a nucleus into a soup of loose Quarks? If you turn this effect off, or the Quarks leave the AoE, what happens? And what is up with all the energy you're moving around to make this possible? My best guess is, other than being extremely interesting for Physicists, you're Quark soup will either explode, showering the surroundings with Pions and their decay products, or they will recombine into some kinda plasma or slag. Keep in mind that Conservation of Baryon Number is apparently a thing, so dissolving a few Protons without some new Baryons to maintain the balance could have weird consequences and absurdly high energy costs.
One thing these keep coming back to is conservation laws. If you're altering a force-field, you're altering the energy of the system. This is particularly nasty for Gravity-bending, where E=AR^2 * 3.5, where the final unit is the amount of energy put out by the sun in 1 second. I like to handwave this away by hiding the energy and mechanism in mumblemumble higher dimentional physics mumblemumble, but exactly how that's dealt with here dramatically changes the results. If you're hiding the energy when you create a Strongless pocket, your Quarks are free to float around until they manage to decay via the Weak force (which should probably be faster than standard Neutron decay, but I could be way off), and evaporate due to the resulting distribution of electric charge, and reforming into Pions once they're out of the AoE. If you don't hide the conservations, the process will generate an equal number of Baryons, and conserve electric charge and Lepton number while doing so.
To bring it back to where this started, and less head-splitty particle tricks, Delta baryons decay via the Strong force. Delta+ and Delta0 are more or less Protons and Neutrons with very roughly 1.25× the mass, tied up in Strong charge. They decay on the order of 5×10^-24s into Pions and nucleons. There are the Delta++ (UUU) and Delta- (DDD), which always struck me as cool but hard to find a use for. If you can keep Deltas stable, perhaps even inside nuclei, you've basically made your atoms 1.25× as massive without obviously changing their chemical properties (temperature, though...). And when you let go, even if they decay into their original form instead of the occasional charge mishap changing Carbon14 into Nitrogen14, the energy will come out as Pions, which end up as Gamma Rays. Whatever shenanigans you get up to with Delta matter, it's going to make quite the mess when you're done. And you can get the necessary Pions from Cosmic Rays, especially if you have a Weak Manipulator to help. Manufacture that, and you just invented batteries that can charge off Cosmic Rays.
Oh, and just in case it matters, we have Gluons as the carrier particle for the Strong force. They always sounded more substantial and less virtual to me, as compared to W bosons and Gravitons. Pions were initially considered Strong carriers, since they are the primary carriers at the level of Protons and Neutrons, I think that's kinda like treating Electrons as the carriers for electromagnetism. So if you're messing with carriers instead of fields, you'd be dealing with the notoriously sticky Gluons. This probably looks a lot like modulating field strength, though.