Yes you can. You will need to fashion a conversion track anytime you go from one to the other. Why they do not make conversion tracks ready to go I don't understand. They might be pricey but would make using multiple codes much easier and more realistic.
Why they don't get on the same page with the codes is the bigger question. Code 55 ought to be N scales standard, with code 40 as the "alternative for scale reasons". Two steps forward one back! I figure by the time I'm dead they all get on the same page. Lets see we have the attrocous code 80, code 65, code 70, code 55, code 40 and who knows what the other multitudes a track manufacturers in Europe and Japan.