I red the SS first, but then I red TSoY and loved every piece of crunch and most of the fluff. So, in what do the games differ? What rules should be changed to "update" TSoY?
Thanks for your attention and answers.

I changed practically nothing, at least from my own viewpoint. The SS system is flexible enough that you can use the TSoY crunch directly; backwards compatibility was so important in writing TSoY that I didn't even think about it; it was obvious to me. Doesn't mean that I think that TSoY is perfect, of course.

You'll have a more complete answer after Gencon, as that's where I will be publishing World of Near, my new TSoY sourcebook that updates the setting for SS rules and my tastes. Feel free to order it once I have a moment to update the webpages to the fact; it'll be a most complete answer to this question.

On paper, the one thing that is more explicit is Effects, which you can already find under the guise of specialized systems in the Revised TSOY rules (ammeni poison rules and to some extent three corner magic). Also, some details in the conflict system changed, namely what happens on a draw between opponents (pay pool points or drop out of the conflict, GM uses this as 'turning point').

Converting TSoY crunch to SS has been done by a friend of mine, mostly it was moving rules texts to use Effects to explain stuff that was clunky before.

Klaus, do you know the german versions of both game texts? They might help you compare and come to your own conclusions.

I'm that friend that Harald is refering to, and the conversion can be found in German in Tanelorn: http://tanelorn.net/index.php/board,350.0/sort,starter/desc.html (look at all topics started by Skyrock with the tag "[Solar-System-Update]"; it's pre-sorted for you)
It isn't complete as it has only been done for a forum game including Maldor and Quek, but it should give you a headstart for all races and those two cultures until "World of Near" is available (assuming that you speak German, which I would assume from your name).

I think Harald has translated and forwarded the stuff to Eero, but I have no clue if any of that affected or landed directly in the final product of "World of Near" (especially as a three-stopover translation German=>English=>Finnish is bound to gain some deviation on its way).

I thank everyone for their answers. ^_^ Unfortunately, I don't know German and my nickname derives from arcane events that took place during my childhood (ok, I just saw the cover of a comic named "Klaus, Prince of the Undead" and used "Klaus" as a nickname since them :-P). Is there an English version of the converted rules?

Maybe Harald or Eero do so yet.

I've been too busy with coming up with the conversions in time for the game to translate them as well, and now with World of Near just around the corner, my motivation to do so would be close to nil.
I might pull out selected parts to compare them with the finished product, but as I strived mostly to stick as close as possible to the general secrets in SS, I wouldn't expect any revolutionary deviances from this angle, unless Eero has changed any existing splat-specific crunch on purpose.