From my experience one of my vendor had to change the spring rate of the hanger due to the additional load at the support. Of course this changed my calculations completely.
The spring hangers have some limitation in minimum and maximum loads for particular spring rate. The code is requiring maximum 25% of load/displacement change. So you need to watch all these in your calculation. Caesar II does it for you. But earlier versions of Caesar II did not add the ancillary weight. So vendor somehow have to do some adjustment.
However, you can put new spring rate and ancillary weight (you can put a flange to represent the weight in your case) into your analysis, check if the system is acceptable with the new loads and spring rates (if changed). Otherwise what is done may be creating problem. Do your analysis if not satisfied talk to your superior for corrective action.

Hope it helps.

Ibrahim Demir