I did not find the option as mentioned in other answer. May be it is updated now, but this worked for me:
Go to settings in Trello then
Go to your Atlassian account option
In Security option you can find the option of change password on top
Also consider, the bookmarklet generator at: https://trello.com/en-GB/add-card
Currently, the bookmarklet sends you to a link a bit like this:
If you can control the content of url you can probably control what ends up on the card.