Miguel Herrera has been fired as Mexico coach following allegations that he punched a television reporter.
Former Arsenal midfielder Abou Diaby has rejected an offer to join West Brom in favour of finding a new club in France.
Seaborne has won three and drawn one of the four matches he has played in since making the temporary move to The Valley.
The 25-year-old was forced to sit out the final match of his original loan spell, last Saturday's 2-2 draw against Brighton.
But Seaborne will get the chance to extend his unbeaten run in the Charlton team after a fresh deal was struck.