Wireless Joint

Is there a program to pull the firmware of the modem,
modify it and add some codes?

more info is needed for a proper answer such as, which part of the firmware, this devices firmware has 31 partitions some being mbn, some img, and some triple layered ubi, ( ubi over ubifs over mtd)
but if you mean like a one click tool or something the answer is no, you have to dump then decompile or unpack depending on which file type you are working with then make your edits with the proper tool then repack back to factory specs and then reload it.

I wanted to change the internal interface of the modem by adding some modifications such as changing the image and changing some icons
The format is spk

I see, ok so if you are not familiar with the things I wrote about in my previous post, you would be much better off if you are just needing to change some images to make your project on a live filesystem and not fool with all the work of the previously mentioned method