user67: This question is a sequel to  an earlier one . Just as in the openings, computers dominate endgames.   Endgame tablebases  provide an exhaustive analysis of endgame positions with a small number of chessmen. The undesirable side-effect is that  optimal endgame moves  are often extremely difficult  for an endgame-expert to understand (see the last post by Bill Dubuque in the link above). 

How has this phenomenon changed grandmasters' preparation against computers?  

For example, they may not allow a game to continue till the endgame when playing against a computer, unlike a human opponent. Or they may avoid endgames with complex variations. 
Note that the endgame allows exhaustive search, and lacks exploitable phenomena like the horizon effect .

user1161: As has been stated in the comments GMs don't compete against computers very often. They more often use the computer to help analyse their own games, especially to help find "computer moves" by which I mean obscure unnatural looking moves that they didn't/wouldn't find in the game but which are tactically sound. 
The endgame in particular is the part of the game where gameplay methods are well established and it actually comparatively easy to see who has the advantage and how the game will end. In many GM games they resign before I would have even been able to tell we had reached the endgame.
In studying endgames the advice I have seen included in the commentary from a GM that came with Chessmaster 8, and in some books, was to practice recognizing the weapons (ie pin, double check etc) in actual endgame positions, learn the basic rules to help speed calculations in the endgame. These are such things as can the king get into the square defined by the diagonal from the pawns position to the back rank, if he can - and no other pieces can interfere - he can stop the pawn promotion, if not he can't, opposition, etc. 

67: <p>This question is a sequel to <a href="https://chess.stackexchange.com/questions/137/has-ai-changed-opening-theory-and-if-so-how"> an earlier one </a>. Just as in the openings, computers dominate endgames.  <a href="http://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=2&amp;ved=0CG4QFjAB&amp;url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEndgame_tablebase&amp;ei=NJcUUP_JEYnG6AH494HAAQ&amp;usg=AFQjCNHonUCR25059VSw4B5eYIJ5tAZOJg&amp;sig2=or7QnMJkpHPE583udnm-vw" rel="nofollow noreferrer"> Endgame tablebases </a> provide an exhaustive analysis of endgame positions with a small number of chessmen. The undesirable side-effect is that  optimal endgame moves  are often <a href="http://tiny.cc/odq6hw" rel="nofollow noreferrer">extremely difficult </a> for an endgame-expert to understand (see the last post by Bill Dubuque in the link above). </p>

<blockquote>
  <p>How has this phenomenon changed grandmasters' preparation against computers?  </p>
</blockquote>

<p>For example, they may not allow a game to continue till the endgame when playing against a computer, unlike a human opponent. Or they may avoid endgames with complex variations. </p>

<p>Note that the endgame allows exhaustive search, and lacks exploitable phenomena like the <a href="http://en.wikipedia.org/wiki/Horizon_effect" rel="nofollow noreferrer">horizon effect </a>.</p>
 1161: <p>As has been stated in the comments GMs don't compete against computers very often. They more often use the computer to help analyse their own games, especially to help find "computer moves" by which I mean obscure unnatural looking moves that they didn't/wouldn't find in the game but which are tactically sound. </p>

<p>The endgame in particular is the part of the game where gameplay methods are well established and it actually comparatively easy to see who has the advantage and how the game will end. In many GM games they resign before I would have even been able to tell we had reached the endgame.</p>

<p>In studying endgames the advice I have seen included in the commentary from a GM that came with Chessmaster 8, and in some books, was to practice recognizing the weapons (ie pin, double check etc) in actual endgame positions, learn the basic rules to help speed calculations in the endgame. These are such things as can the king get into the square defined by the diagonal from the pawns position to the back rank, if he can - and no other pieces can interfere - he can stop the pawn promotion, if not he can't, opposition, etc. </p>
