cancel transaction in MultiBit Classic
Control over money in Bitcoin is defacto[1] binary: either a transaction has been confirmed in a block and the money has been signed over, or the sender remains in control of the money. Hence, when you export the keys from MultiBit and import them to another wallet, you will be able to overwrite your previous transaction by issuing another transaction transferring the money somewhere else (unless the new platform is aware of your previous transaction and forbids doublespends).



[1]The only exception to this is the option of the recipient to create a child-pays-for-parent transaction which provides a sufficient aditional transaction fees to compensate the low fee of its parent. Still the money is only signed over once the transaction is in confirmed in a block though.