Well, as you could tell by my away message, I was at school. Tuesday\Thursdays are my long days, and today was especially bad since I had an evening exam, but MWF I've only got a morning class and I'm home. I should be easy to reach on those days, I think.
While working on my Mega Man 7 run I did attempt to use previous work (either from the first version or redone parts from version 2). I did it all using QBASIC, though. ^.^;; (I'm more used to the QBASIC file handling system than any other language).
Anyways, the SNES9X file format isn't too complex (for a 1 controller run, anyways). Just a 197 byte header and 2 bytes per frame. (Well, 197 bytes if the number of frames SNES9X tells you a movie has is the actual number of frames it has). Splicing old movie with a newer redone part can be done like this:
Read from the newer redone part till you know you're just past the improved part and are at a spot that you know is in the old part. Then skip over the frame data from that old part until you reach that known part and start copying from the old run. Which of the two headers should you use? I'd say the longer one, but make sure that one has a couple of extra seconds of data just to be safe, I guess.
Also, speaking of safety, I made sure I didn't stand to lose anything while doing this by making copies of the files I was going to work with, working with those copies, and having my splicing program create a third program instead of overwritting any of the other two.
Now, it works...it gets the keystrokes over...but random factors may make it totally useless. I was able to do the splicing in my Mega Man 7 videos but the random factor in it was...well, too random and every splice (entertainingly) desynced.
Here's an example of a failed attempt:
http://www.kraftfam.org/~erk/misc/mm7.zip
(it includes a save state to jump to Wily Stage 4)
In particular, I tried to splice the Freeze Man battle from my first version into the second version. I mean, Freeze Man didn't seem to be all that random, right? Well, you can see the result.
So, splicing to try and fix this one small part might not work, but then again it might. Super Mario World doesn't seem like it has too much randomness in it, but who knows. It could be like Freeze Man and suprise me how exactly it is random, hehe.