Blender addon to add a prefix to the blend file when saving.

file_prefix.py

# script made in response to
# http://blender.stackexchange.com/q/40436/935

bl_info = {
    "name": "Save File Prefix",
    "author": "sambler",
    "version": (1,0),
    "blender": (2, 71, 0),
    "location": "File->Save Prefixed Blendfile",
    "description": "Add a prefix to the filename before saving.",
    "warning": "beta",
    "category": "System",
}

import bpy
import os

# adjust this function to return the prefix you want
def fn_prefix():
    return 'xx12345xx_'

class PrefixFileSave(bpy.types.Operator):
    """Set a filename prefix before saving the file"""
    bl_idname = "wm.save_prefix"
    bl_label = "Save Prefixed Blendfile"

    def execute(self, context):
        outname = fn_prefix() + bpy.path.basename(bpy.data.filepath)
        outpath = os.path.dirname(bpy.path.abspath(bpy.data.filepath))
        return bpy.ops.wm.save_mainfile(filepath=os.path.join(outpath, outname), check_existing=True)

def menu_save_prefix(self, context):
    self.layout.operator(PrefixFileSave.bl_idname, text=PrefixFileSave.bl_label, icon="FILE_TICK")

def register():
    bpy.utils.register_module(__name__)

    # add the menuitem to the top of the file menu
    bpy.types.INFO_MT_file.prepend(menu_save_prefix)

    wm = bpy.context.window_manager
    win_keymaps = wm.keyconfigs.user.keymaps.get('Window')
    if win_keymaps:
        # disable standard save file keymaps
        for kmi in win_keymaps.keymap_items:
            if kmi.idname == 'wm.save_mainfile':
                kmi.active = False

        # add a keymap for our save operator
        kmi = win_keymaps.keymap_items.new(PrefixFileSave.bl_idname, 'S', 'PRESS', ctrl=True)

def unregister():

    wm = bpy.context.window_manager
    win_keymaps = wm.keyconfigs.user.keymaps.get('Window')
    if win_keymaps:
        for kmi in win_keymaps.keymap_items:
            # re-enable standard save file
            if kmi.idname == 'wm.save_mainfile':
                kmi.active = True
            if kmi.idname == PrefixFileSave.bl_idname:
                win_keymaps.keymap_items.remove(kmi)

    bpy.types.INFO_MT_file.remove(menu_save_prefix)

    bpy.utils.unregister_module(__name__)

if __name__ == "__main__":
    register()