Hi Silivio,
Can you please clarify whether enternal TR mean "created outside the ChaRM in Devlopment System" or "added in imort buffer of Development System".
For option 2 : I will recommend to create new TR in your dev box and after adding external TR in Dev import buffer, merge the object in new blank TR. Than you can continue with CD by moving that TR.
Since durig "Pass Change to Test", it release TR and import in QAS. Bt in your case TR is not available as released TR.
For Option 1 : You need to register TR through task list and than can b added to change document. Only thing we need to make sure that TR should be under modifiable state otherwise cann't be register in SolMan.
Regards,
Piyush Jain