Atletico Madrid have signed full-back Cristian Ansaldi on a season-long loan deal from Zenit St Petersburg.
Ryan Inniss is expecting to be sent out on loan again by Crystal Palace and hopes to test himself in Sky Bet League 1.
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.