What mining parameters are not modifiable with ASIC miners? When ASIC mining devices ship, what parameters of mining become hardcoded? How would these ASIC mining devices respond to any changes to mining procedure / algorithms?
Very little of transaction validation logic is done in the ASIC. All that they do is take a block header, rapidly increment the nonce, and see if the hash that pops out is anywhere close to the target. So, as long as the block header doesn't change, none of the ASICs need to change.
Nonce
The 4-byte nonce field might need to change in the near future, because you can only have 4 billion distinct hashes every second. That might seem like a lot, but with ASICs getting 100Ghash/s, it gets a bit awkward. One way around it is to make 25 different coinbase transactions, thus getting you 25 different block headers. You then give each twenty-fifth of the ASIC a different block header. Despite all this, lengthening the nonce field is probably more trouble than it's worth, given that it would require a hard fork.