(I thought Does new Star Wars continuity only affect post-Jedi EU? was going to be along these lines on first read of the title, but this question is different.)
Is there any on-record statement about whether the first six Star Wars movies will be affected by the new films? Might there be some retconning, insertions, new effects etc. added to the original six (and especially the original three) films to tie into or make the new films work?
I don’t know of any direct statements on the issue, but the press release linked from the other question you mentioned does say:
...the six Star Wars episodes, and the many hours of content... produced in Star Wars: The Clone Wars... are the immovable objects of Star Wars history, the characters and events to which all other tales must align.
Of course, that didn’t stop George Lucas from endlessly f—ing around with the original trilogy every time they got re-released. But it does suggest that new Star Wars content is expected to be consistent with the existing movies and Clone Wars.
And it’s worth noting that Fox still owns the distribution rights to the existing films, so Disney at least can’t can’t unilaterally release amended versions of the existing movies (though history suggests that Fox would have no problems with putting out Super Edition Hyper Fighting versions of the existing films with twelve seconds of amended footage that fits in slightly better with the new trilogy).
