1. Can u change default med pack to another ? (model like on harvest event)
2. How do i load models in my map like not only me can see it, but and others players who plays this map. (The same with textures)
3. Can i change respawn time for a medpack?
For #'s 1 and 3, I don't know myself. For #2, use a program such as PakRat (use Google to find it) to pack your custom textures and models into the .bsp file for your map before distributing it. If you get it and aren't sure how to use it, I'd imagine there are tutorials around here that should be able to help you.
#1. Double-click the item, click "Model," and browse for a different model like you would for a prop. (You need to have the alternate model files already unpacked to the /models/ and /materials/models/ folders, of course.) It won't show up any differently in Hammer, but it will work when you compile and run the map.
Put the vmf file into your C:\Program Files\Steam\steamapps\username\sourcesdk\bin\orang ebox\bin\prefabs folder, then it'll appear under prefabs. Use with great care, as most servers don't like you messing with their variables, and some crafty players can exploit this.