Modifying the libraries carries with it some level of responsibility. It is generally expected that you will not wish to do this until you have quite a lot of experience (see Appendix A). However, just as a guide we will provide here a quick summary of what would be involved.
Putting modifications to existing files back into the library simply involves copying them into the appropriate locations and recompiling the library. The main issue to be aware of is that you have not redefined the functions so that they no-longer work as intended in other parts of the library.
If you have new C files and headers then you will need to make sure that these files use naming conventions which are appropriate to the part of the library you wish to place them. Header files need to be indexed using the file locations as they will exist in the library. All function calls need to use the most appropriate library routines, rather than any home grown ones that you may have used during development (this requires some familiarity with the existing libraries as there is no simple way of telling people what they should have used). The last thing to do is to add the required software licence or copywrite, depending upon the required level of protection.
Once the files have been added to the library you will need to update the CVS repository to maintain them and also modify the library Makefiles to include them. All modifications should be stored in the appropriate library Change Log and then the whole lot committed back to the CVS repository. Finally, the repository should be checked out (from scratch), in order to test the build process and the new functions tested on example data.