I'm pretty sure the 15-2138 can be upgraded by .wav file. But it can't use a .wav file that was created for another model remote. I'm pretty sure neither OFA nor RS distributes .wav file for the 15-2138.

Any JP1 expert (including myself) could use the JP1 software to create a .wav file for CBL/0817 for the 15-2138. But I don't have time at the moment.

You'd get a better upgrade (better choices over which functions go on which keys) if you made that .wav file yourself using the free JP1 software. But that's rather much for a beginner to learn how to do.

Also, Alfaman is correct about the NEC code format used in CBL/0817. There shouldn't be any problem learning it, other than the fact that you'll probably run out of learning memory before learning all the functions for a cable tuner. Since it blinks twice at the end, you aren't out of memory yet. Maybe Alfaman is also correct about what is going wrong there. Pressing the original remote button before the 15-2138 is ready to learn would have those symptoms. I have no clue whether it is easy to accidentally press the original remote button too soon.