How convert a mnemonic phrase back and forth between different number of words? I'm relatively new to cryptocurrencies in general and I've tried using Bitcoin and a few altcoins, but it always bothers me that some digital assets are not available in all wallets. To my understanding, I could use the same mnemonic phrase in all wallets, even if some assets are not listed, if that's true I wouldn't have to store a different list of words for each wallet. The only problem is that most popular wallets support a different numbers of words in the mnemonic phrase. Is it possible to convert back and forth between say, for instance, a 24-word phrase to a 12-word phrase, and what tools can I use to make the conversion?
Is it possible to convert back and forth between say, for instance, a 24-word phrase to a 12-word phrase, and what tools can I use to make the conversion?


No, that is not possible. The mnemonic words represent an entropy, for example the 24 word mnemonic phrase represents 256 bits of entropy while a 12 word mnemonic represents 128 bits of entropy. These mnemonic words are passed to a PBKDF2 function to generate a seed that will then be used to generate master keys for different tokens. It's also important to note that if you use a passphrase to your wallet, that passphrase will be used as a 'salt' in the PBKDF2 function and will generate a completely different seed, had you not used a passphrase. 


  To my understanding, I could use the same mnemonic phrase in all wallets, even if some assets are not listed, if that's true I wouldn't have to store a different list of words for each wallet


Care has to be while doing that as many wallets use different paths of master key generation. If you use multiple wallets interchangeably, try to note the derivation path. For example, say hardware wallet A uses m/49'/0'/0' as the path, it will generate completely different addresses as compared to a wallet that will use a m/44'/0'/0' derivation.