Now I can't kick start bike cause shifter rod is frozen shut.
At first I though your gear lever was jamming,and not able to shift in or out of gear.That might happen if you siezed a gear onto the mainshaft or layshaft;and that can sometimes be fixed for the price of gearbox gaskets and the use of a press to move the gear off the shaft.
Reading further down,it appears that only the kick-start lever is jammed.You can select neutral,and it sounds like you can also select second gear.
If you can push the bike along in neutral,the output sleeve gear is turning and the layshaft is also turning freely.The mainshaft won't be turning,as you push the bike,until you engage a gear.
If you engage a gear ,4th or 5th would be best,can you push the bike and turn the engine with the sparkplugs removed?That might eliminate some possible causes of your problem.
If this really is a gearbox problem,it would be good to know the model and if it is 4-speed or 5-speed.Are you really putting ATF (transmission fluid) into the gearbox,or are you using gear oil?