I know this is very old case but I am reply to express my understanding and bring some clarity.

I believe this is the case of cold pull and two separate stress analysis to be carried out to mitigate load stepping.
For first cycle:
1) Piping system with support acting normally.
For rest of the cycle:
2) Piping system with cold pull by 250 mm and limit stop which is really large value. This will generate tremendous end reaction.

Is it correct approach?