How do I change the mouse's i-beam cursor in Xcode 7.3
Here's the solution that works for me thanks to a GitHub link provided by @aldryd:


https://github.com/egold/better-xcode-ibeam-cursor/issues/16


GitHub user sokobania provides the following steps:


Download ThemeEngine from: https://github.com/alexzielenski/ThemeEngine
Run ThemeEngine in Xcode and you may be presented with a few errors.


Failed to code sign "ThemeEngine".  


Just click Fix Issue

Nullability specifier '_Nonnull' cannot be applied to non-pointer type 'NSString'; did you mean to apply the specifier to the pointer?


Allow Xcode to Resolve


We'll need to remove some derived data from Embedded Binaries. Click your root application > Targets > General > Embedded Binaries and remove the top item:


Run ThemeEngine and select "Open Document", you'll need to locate your Assets.car file in Xcode here:

/Applications/Xcode.app/Contents/SharedFrameworks/DVTKit.framework/Versions/A/R‌​esources/Assets.car

Once loaded, find DVTIbeamCursor in the list and drag your IBeam of choice over Xcode's default Ibeam.



I like use the Ibeam provided by @TheTC: 
dracoventions.com/images/external/TIbeam.tiff
Select "Save As..." and overwrite Xcode's Assets.car file with the new file. I had to save the copy to my desktop and then drag the new Assets.car file into the Xcode folder to overwrite.