Disabling the lane change signal feature of a 2014, 2015, 2016, 2017 Corolla
FakeMoustache actually should get credit for answering my question, but he posted it as a comment and an answer should be posted here.

[Edit 12/5/2018: I have now done this successfully with three Corollas.  Works great!]

Just in case someone has a 2014, 2015, 2016, or 2017 Corolla, below is what I provided to the mechanic to make this simple modification.  Even as an experienced driver, I don't like the lane change feature.  As FakeMoustache stated, use any of diodes 1N4001, 1N4002 through 1N4007.  I used 1N4007's, but probably should have used 1N4001's since the leads are thinner and easier to work with.

Notice the black wire doesn't necessarily have to be cut, but I find it easier than stripping and splicing mid-wire.

Also notice there are two pink wires.  Don't splice into the wrong one!  See the illustration.