- Open Player.img with the ImageTool (File>Open)
- Search for sixtyniners.txd (Edit>Find)
- replace the TXD-file with the new sixtyniners.txd (right click>replace)
- close ImageTool and start GTA SA

ingame:
- drive to ProLaps and buy the 69ers Shirt
- enjoy

My first upload on gtainside.com.