Is there a way to test (if you still know) your Mist wallet password without making a transaction?
Make sure Mist is running.
Run this command to attach to the geth daemon:
personal.unlockAccount('ADDRESS', null, 1)
You will be asked for the password.
This command will return true and unlock your account for 1 second if the password is correct. If it's not you will get an error message:
Error: could not decrypt key with given passphrase
It's possible! But it requires using command line tool Geth
You can update an existing account on the command line with the update subcommand with the account address or index as parameter.
geth account update b0047c606f3af7392e073ed13253f8f4710b08b6 geth account update 2
The account is saved in the newest version in encrypted format, you are prompted for a passphrase to unlock the account and another to save the updated file.
This same command can therefore be used to migrate an account of a deprecated format to the newest format or change the password for an account.
For non-interactive use the passphrase can be specified with the --password flag:
geth --password <passwordfile> account new
Since only one password can be given, only format update can be performed, changing your password is only possible interactively.
Note: Account update has the a side effect that the order of your accounts changes.
After a successful update, all previous formats/versions of that same key will be removed!