getnewaddress vs. getrawchangeaddress
The rawtransaction interface accepts and returns "raw" hex encoded p2p compatible transactions. Using the non-rawtransaction methods (like sendtoaddres, will not give you the possibility to inspect or alter the created bytearray.
The getrawchangeaddress method will retrieve a key from the keypool and return its pubkey (encoded into an p2pkh address). Unlike getrawchangeaddress, gewnewaddress will create an address book entry that will allow you better ways to inspect/distinct what funds you have received with that address and therefore increases the chance of a reused address.
You should use getrawchangeaddress if you like to use the given address as a change output for your rawtransaction.