If your centers don't unbolt from the ring then the answr is no, I'm pretty sure you cant change the offset the only thing you could do to widen them would be to use longer wheel studs and have some spacers machined.
If they're R4 tires, solid centers welded to the rims, then no. These are out as far as they can go. I haven't seen the rims with ag tires to know if they can be unbolted as somguyss mentioned.
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You also want to measure the offset on both the inside and outside of the wheel. If the offset is greater on the inside, swapping the wheels side to side might be worthwhile. Remember, R-4s are uni-directional, so it would have to be a side to side swap.