Override {baseSiteId} value in commerce webservices

Hi,

Can you please let me know how to override this {baseSiteId} value that comes in the url of a commercewbservices.

say - https://localhost:9002/ulcommwebservices/v2/{basesite}/products/search

works with https://localhost:9002/ulcommwebservices/v2/powertools/products/search

how to override this value with some custom value ? Also please let me know if this {basesite} is a mandatory value ? Commercewebservices will not work without providing a value for {basesite} ?