Could ASICs be used to mine a "BitcoinX4" blockchain? Bitcoin, on average, has a block every 10 minute. There are advantages (pdf) to having a higher "clock rate", e.g. Litecoin's block every 2.5 minutes. I call "BitcoinX4" the theoretical blockchain that is achieved by speeding up block creation time (hardfork), without affecting the total number of coins (block reward reduced by a factor of 4).

It is conceivable that at some point in the future, a "split" or "hard fork" will be made in Bitcoin, such that its blocks will be generated with a different (higher?) frequency, possibly while keeping a mining majority. For this to happen (hash power majority), ASICs need to be able to crunch the new "BitcoinX4" chain.

So, my question - are the known ASICs today compatible with changing the block speed?
Any mining device can be used without alteration for mining a specific alt-chain, as long as the chain's proof of work is the same (double-SHA), and the size, encoding and position of the timestamp and nonce fields is the same in a block. The latter ensures that devices that increment those fields internally would not be altering other parts of the block header. As block speed is not a part of the header but an external constraint put on the specific cryptocoin, ASICs and other devices should be able to mine such blocks without a problem.