The verilog code for the custom component created can be viewed from the verilog tab (mycomponent.v) for the custom component. No verilog file for the custom component created is present in codegentemp folder of the project.
However the .v file for the entire project (myproject) is present in the codegentemp folder for that project.
I did notice the myproject.v in the codegentemp folder. I've been including just that one file in the codegentemp folder and doing diffs on that. This has the advantage of catching the diffs for the entire design, but it is not quite as easy to identify the diffs for each component individually.
Thanks for your help!