How easily can asics be ported over to other sha algorithms?
Application Specific Integrated Circuits are hard set to only do one thing, and in the case of bitcoin ASICs, that's SHA256 hashes. You cannot re-write the software, you would need a new circuit built that only does SHA1 or whichever hash you're looking for. 

https://en.wikipedia.org/wiki/Application-specific_integrated_circuit