You definitely have to sign and execute the transaction after using merge or split coins. The methods you're using construct the transaction as unsigned, so you need this extra step afterward to sign and execute it.

Yes, as previously mentioned, you need to sign and execute the transaction after merging or splitting coins. Unlike in Solidity where constructing, signing, and sending the transaction often happen simultaneously, in your case, these steps are kept separate. This separation allows you to review everything before signing, making the process more secure.