Transport Tycoon Forums

You need Git or HG for that.

As a workaround ...
-Pull diff from modified patchpack.
-Compare original and modified patchpack.diff in file comparison program while applying only the difference to clean trunk. (Manually.)
-Pull diff.
-Done.

If you have a diff program, you can get a diff from two directories.

However, it is in the somewhat longer run probably better to get HG, and learn how to use its patch queue (mq).

Sounds like a task for hg queues. But any version control system would probably do.