I often have the problem that a message gets stuck in the mail queue and I want it to be bounced to a certain address.

You can do this using a combination of four command line options, like this:

exim -Mf   14Fdlq-0003kM-00
exim -Mmad 14Fdlq-0003kM-00
exim -Mar  14Fdlq-0003kM-00  new@ddress
exim -M    14Fdlq-0003kM-00

The first command freezes the message so that a queue runner won't start to deliver it while you are changing things. The second command marks all existing recipients as delivered. The third command adds a new recipient, and the fourth command forces a delivery of the message, which will cause it to be delivered to the new address, and then deleted.