So, its possible to play offline... But you must have already downloaded Tekkit on PC. This way is simply locked access of Technic Launcher to internet and activate offline-mode.
You must to have Hex-Editor and archiver.
So...
1) Open technic-launcher.jar with archiver and find file org/spoutcraft/launcher/Main.class .
2) Extract it in any folder.
3) Open Main.class with hex-editor and find nearly address 000018E1 this sequence of byte:
001503B4
4) Change it to:
001504B4
5) Save Main.class and rewrite it in the archive.
6) Launch technic-launcher.jar. You'll see the button "Offline Mode".
Of course, you can not update the game, but you can play. If you want more - to buy the game.
