from copy import deepcopy
from numpy.random import default_rng, PCG64, Generator

def custom_deepcopy(rng):
    orig_bitgen = rng.bit_generator
    if isinstance(orig_bitgen, PCG64):
        # `seed=0` is faster than `None`, and we don't care because we override the state next
        new_bitgen = PCG64(0)
        new_bitgen.state = new_state = orig_bitgen.state.copy()
        # Copy the one inner dict manually, all other values are immutable
        new_state["state"] = new_state["state"].copy()
    else:
        new_bitgen = type(orig_bitgen)(0)
        new_bitgen.state = deepcopy(orig_bitgen.state)
    return Generator(new_bitgen)

rng = default_rng()
assert deepcopy(rng).bit_generator.state == custom_deepcopy(rng).bit_generator.state
%timeit deepcopy(rng) # 66.6 μs ± 1.96 μs per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
%timeit custom_deepcopy(rng)  # 22.1 μs ± 335 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)