Power custom field : Change the dropdown value based on transition

[Omprakash Thamsetty]

We have a requirement as follows so look like we can achieve with SIL custom field. Can anyone guide me how I can set following scenarios. 

 I needs to have 2 sets of dropdown values during the Onhold and Cancel transition for one "Reason" dropdown field.

example:

Reason field values when OnHold transition.

• Hold from customer

• Hold from dev

  Reason field values when Cancel transition.
• Cancel by customer
• Cancel by DEV

How to write code in sil or how to find the transition in SIL programming ?

Thanks,

Om