hi, I'm currently playing on more than one server. And I don't want to install the whole thing everytime I play a new server.
Some people told me that I can download the sclientinfo and replace my previous server's sclientinfo. It's not working for me. I somehow manage to login, but my character is not there...or my character has some weird name/numbers, and can't go in and play.
You need to understand how the client works, and how private servers work.
The problem you see seems to be a client version mismatch. The kRO clients before December of last year are incompatible with the clients after that date. If the server supports the older clients, it can't support the newer ones and viceversa (this is configured at the server side). You need to know the "date" of the client you wanted to use to see whether you need to get a newer, or older, client to make it work with the server in question.
But modifying the sclientinfo is only half the battle... servers usually have grf files, and different servers have different grfs for their own customs. Playing without the server's grf (or another server's grf) could mean that palettes look weird/different, custom items don't show a sprite nor desc (or they could even crash you when you try to see/use them). You would also need to know how to configure the client to read different grf files based on the server. You should check the eAthena boards, under client tools there may be something to help you set up multiple server selection (and "client support" over there is a good place to ask for help, the eAthena boards has a lot more traffic than RMS as far as I know).