As far as I can remember, the only thing that needs to know the name of the lldb binary is the swift driver when it starts up the Swift REPL - since the REPL is actually just a mode of lldb. Other than that lldb doesn't know its name in any other places I can find other than in the usage string printed out for "lldb --help".
But lldb actually ships with a bunch of binaries (lldb-server, lldb-argdumper, etc.) Do you only need to change the lldb binary's name, or do you need to change the name of all duplicated binaries and/or libraries?
If the former, then this should be pretty straight-forward. Otherwise it gets a little more gnarly. There are a couple of helper apps lldb needs to find (lldb-rpc-server & lldb-argdumper). If you had to change the name of modules you may need to play tricks to get the python module to be called lldb. Changing the name of the module would break the testsuite & scripts that use the module. The test suite does launch lldb in a few places so we'd have to fix that.
But I think all this is just work, it shouldn't be hard. BTW, I'm not weighing in yet on whether I would love having the name changed yet. I have to think about that a little more. But it would be doable.