You can remove "reserve" address(es). If the wallet was created by MultiChain, there should be only one "reserve" address. This address was never used by the wallet. (It will be the next address created by getnewaddress).
But you have to do this every time you dump the wallet. If address was created by wallet A (and was never used), then wallet was dumped (with "reserve" address) and imported to wallet B. It can be used by wallet B. So, when you remove "reserve" address and import dump file to wallet C - you can miss some transactions created by B. If you always remove "reserve" address from dump file - it cannot be used by other wallets.
As for the "change" address, MultiChain always sends change to one of the addresses in inputs (at least for walletdbversion=2). So, you should not see "change" addresses in the dump file.
If you see more than one "reserve" address or "change" address - please let us know which version of MultiChain are you using.