YES, you can transition from new copper to old galvanized, but just be sure the plumber uses the right fittings to prevent corrosion.  

Quote from @Margaret Blythe: Quote from @Michael Borger: In coastal areas like Hawaii, where I invest (in addition to Alaska), you have to be mindful of environmental hazards -- hurricane susceptibility, erosion, salt corrosion, etc.

If it is roots, joint corrosion, etc we get it chained which has some risk but clears the drain of anything except pipe breakage that would cause a clog.Good luck

Internal corrosion in the lines can and will affect the pressure and draining capabilities of the plumbing system at some point in the future.

In Mass, that means that all components are double-wall, non-corrosive (fiberglass). 

For example, they might say something like "There is significant corrosion and to repair I might end up damaging other things.

I think if there is one positive to come out of this housing market it would be that, the market of the 2010’s where everyone lived in 10 major metros was really corrosive for the country imo, to the extent we can revitalize areas & spread out, get some regionally back I think it’s great. 

Personally, if the pipe fittings were not leaking, and did not show signs of significant corrosion, then I would probably leave them alone until there was an issue.

Common locations for supply lines to fail are where male threaded galvanized pipe is threaded into brass or copper valve and fitting bodies  (due to galvanic corrosion)  and hot water lines will rust up so badly as to start restricting water flow or begin leaking a decade or two before the cold side fails similarly.   

A property we are furnishing is on an island surrounded by saltwater so corrosion is a serious concern.