Question is simple, I want to play vanilla version again before trying 1.13, but I would like that highres tweak while playing.1024*768 is much nicer than 640*480 : ).
Is there somewhere only the highres mod without the 1.13?

Me too.

The nice part about 1.13 is that it is not directly modifying the core JA2 data therefore you can launch the vanilla game even with the 1.13 mod installed.

To play in higher resolution you can launch the game via the ini editor and change the resolution to your liking, see screenshot attach.

The Ini Editor should be in the core JA2 directory after 1.13 was installed.

Alternatively there is yet another project (eventually approaching full rewrite) http://www.moddb.com/mods/ja2-stracciatella aimed primary at cross-system compatibility. I haven't used it myself, but as advertised, it tries to be very respectful to the original, although in games like JA2 the line between bugs and questionable design decisions may go very blurred at times, so no guarantees your favourite quirk of the game haven't changed behaviour in that version.

It also is independent from and incompatible by design with 1.13 what is considered too intrusive and much too big blob of strange features by its developers.

Both projects are still actively developed so don't settle for years old "stable" versions but search for the latest in relevant places, Bear's Pit for 1.13 and latest Stracciatella moved to Github for development.

Unfortunately 1.13 Vanilla is bugged (but can be fixed): http://www.rpgcodex.net/forums/index.php?threads/ja2-vanilla-vs-1-13.106743/page-3#post-5550499

Stracciatella seems to be bug free, but unfortunately its higher resolutions don't look nearly as good as the same resolution with 1.13.