Trivia: When Yelena is talking about Alexei wanting to relive his glory days as the Red Guardian, she sarcastically calls him Crimson Dynamo. In the comics, Crimson Dynamo is one of Iron Man's enemies. Ivan Vanko from Iron Man 2 was partly based on this character.
Trivia: This film marks William Hurt's fifth and final appearance as Thaddeus "Thunderbolt" Ross. He died from prostate cancer the following year, and his role was recast with Harrison Ford moving forward.
Trivia: There is an extra scene after the credits with Yelena and Valentina Allegra de Fontaine at Natasha's gravesite.
Trivia: Nat keeps the blonde look and the vest from her sister Yelena, those are in Avengers: Infinity War.
Answer: I can't attest to if the end credit scene was altered, but I can say that it's been Marvel's M.O. to introduce new characters to foreshadow upcoming projects without really giving them much of an introduction. For example, Fury, Thanos, Captain Marvel, the Wasp. It seems this credit scene was meant to tease the audience for her upcoming appearance in the TV show rather than build on who they've already established her to be.
Bishop73