I am still yet to understand what you mean because am confused when you say you want to be updating your portfolio every month, how sure are you that the current crypto you have been holding for one month will give you profit and not loss, the crypto market is one that's very hard to predict and can't know what the future holds for it so I advice you hold your coins for a longer time and keep adding monthly than changing them because it would not be so wise if you do change them after 30 days.