1) To use this library user need not do anything but to just install libsst. when you install libsst, entry will be made in "/etc/ld.so.preload" (if this file does not exist then it will be created). So all the application using the routines exported by this library will link to this library rather then libc.
2) on a system where libsst is installed, you can use the command "ldd" on the executable (the tool you compiled) to see the libraries it is depending. If libsst.so.1 is listed then your application/tool uses this routines.
3) you need not recompile the existing code, Just install libsst library and all the applications using the routines exported by libsst will use libsst.