1). You need to unpack the 316c9986d12cc453a0cd3f9fbf75a7ef.fsh file with BIGgui then open the 316c9986d12cc453a0cd3f9fbf75a7ef.fsh file with fshed once you have that opened highlight the 1st jbck there are 22 of them (obviously) then hold down ctrl+I that will bring up the import window, click on NEW then locate your No.1 back *.bmp file then click on update, if done correctly it should of updated that back pic.
2). Once you done all 22 backs goto (File - Save As) locate the 316c9986d12cc453a0cd3f9fbf75a7ef.fsh and copy over it, make sure its the one you have unpacked the back file are about 57KB packed and about 707KB unpacked.
Note: Editing the backs or most of the fsh and big files packed will give some errors! when importing, it did for me anyway! so i always unpack the files 1st.
Hope this helps. . . . . . .