Thanks Tom. This is the same procedure I got from the Dish How-to page for "Program remote using new remote address" I had done it many times without success before, but went through it once again. As before, it failed with an error dialog saying I wasn't allowed to set the address to the same address as another remote. I.e., it rejected it because TV2 was already set to 1.

Then, on a hunch, I moved the remote slider switch from UHF to IR, and used the above procedure to successfully change TV1 to 3--- the System Info screen showed TV1 at 3 and TV2 at 1. Then, I went through the same procedure again, entering 1 for TV1. This time it worked… no error message and the System info screen shows TV1 & TV2 set to 1. Moreover, both remotes worked. Go figure!