there are two problems: writeable disks, and copy protection. First, you'll never really know if your copy (or original disk) is unmodified. Second, copy protected games can only be played using .ipf-images, which cannot be read in a deterministic way. Either that, or the copy protection needs to be removed, and hacked images are not allowed on this site. So even if the emulator is reliable enough for synced rerecording someday, we'll miss out on most of the best games. :(
The problem with the Amiga is a different one. UAE already supports savestates, and some of the runs on the (now inactive) recordedamigagames.org were using some kind of tool assistance. But most amiga games have some kind of copy protection. Usually invalid sectors on the disks that return different data each time they're read. So, game dumps come in two flavors: * .adf images. They just store the data of reading each sector once, and will thus fail to boot copy protected games. Most games distributed by .adf are cracked, i.e. have the copy protection removed. Tasvideos.org does not accept run on modified games. * .ipf images. This stores the results of reading the disk several times, but it's a proprietary, closed source format made by the Software preservation society. As far as I know, it is not deterministic and cannot be used in a rerecording emulator. Not to mention that we couldn't claim that everyone dumped the original disks themselves: the tool to dump disks in this format isn't public. Thus, while it should be possible to add rerecording to UAE, the list of games we could actually TAS would be minimal.
whether this is activated by the X button or by the Konami code is irrelevant
But to the core of your question, no, having an SRAM-anchored movie would not be enough to avoid using a separate, specific disc. Unless, of course, you allowed for modifying the SRAM to also incorporate a monster, which would allow for any arbitrary type or stats. If you wanted to allow SRAM modification as a means of bypassing using another disc altogether, I think you'd still have to share the appropriate TOC values that would resolve the monster in question. This isn't possible yet, but with a bit more reverse engineering and research probably could be.
FWIW, the Pixie/Dragon "Daina" used by NK in this movie is a good monster, but possibly not the best. It is also not a "special" monster; many different discs have been found that can resolve it. Other stat seeds may lead to a better overall monster, depending on the strategy. It may not even be an optimal monster type, but it's a very wide pool to search through and strategize for.