Hi Aslam
Yes your understanding is ok.
Additionally I think some fine adjustment is done at site to fix the spring with pipe at pre- define force ( called theoretically installed load).
Once we fix the spring it try to maintain same upward load ( unless move up or down) at that point of the piping system.
That is the problem with spring system.
1) If certain case more force at that point expected ( hydro test case) then it will disturb the whole system if spring is in operation. We need some remedy. We lock the spring.
2) In certain case if less piping force at that point expected ( WNC case) it again create problem in whole system ( just reverse in direction than hydro case). We need some remedy .
3) If you closely follow the modified caesar file ( suggested by you) vertical load at spring almost same at spring location because no much vertical movement at spring. But check the load variation at nozzle, Sustain- 64814, Operating -82204 whereas WNC only +4510. Percentage variation of Sustain to WNC very high. In this particular case may be it is still within permissible limit. But may be not in some other case.
For rigid support in any time less load come from piping system is absolutely no problem, If it a spring once you fix it less load or more load come from piping system at that point is equally bad.

Regards
Habib