Post Check In or Deliver changes to source code file
2 answers
Check in is not yet available (some work done for 6.0.4) as an operation ID and in general https://rsjazz.wordpress.com/2012/12/14/do-not-modify-the-triggering-element-in-an-operationadvisor/ means, that you can not modify the SCM data in the deliver operation. You can only prevent a deliver (or check once available).
I confirmed that with the SCM development team.
You can modify files only after the deliver has been done.