How to route signals across to a breakoff tab?
This is a method successfully used for break-away tabs with programming headers:



The points of note are:


Drilled holes for convenient break-away
Traces are 10 mils, with a 6-mil neck at the break line: This provides a natural strain point on the copper trace, so it breaks cleanly right there.
A corner on each trace, each side of the break-away holes. This ensures that even if a particular trace breaks badly, the damage is constrained to the immediate part of the trace up to the corner.


This has worked reliably for a bunch of boards, always broken by hand, not necessarily carefully.