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I'd start with some simple stuff.
Compare mean and standard deviation for the whole frame and a representative subframe or two (don't include any obvious regions with amp glow, bright/dark columns or lots of hot pixels). Any significant differences between the old and new bias frames would flag a change in behaviour.
If you have at least two "before" and two "after" bias frames you can compare read noise. Subtract one before bias from another before bias and you get a frame that contains only the read noise from the two bias frames. Take a representative subframe and calculate the standard deviation. Divide this by SQRT(2) and the result is the read noise in ADU. Multiply by the camera gain to get the read noise in e-. Repeat for the new bias frames. If all was well you'd expect to get similar results.
Cheers,
Rick.
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