Greetings Mr. Yin

I think your suggested program modification is a good one. In the mean time, I have two suggestions:

FIRST:
Instead of your steps 1, 2 & 3, you may save some time by doing this:
1) Use the V/F database to obtain the length/weight of the valve.
2) Having made note of the length & weight, turn off the Rigid specification and change the length of that element to the drawing dimension you refer to (flange + pipe).
2) Use the Break command and define the distance to the new node as the flange length. This provides the two elements of correct length.
3) Activate Rigid on the flange element and enter the weight.
I believe this is a more efficient approach that will save a bit of time and mental effort.

SECOND:
CADWorx/Pipe will let you build the model with less effort, and then create a CAESAR input file from it.
Of course this requires AutoCAD, CADWorx/Pipe and spending some time to get proficient with the program, but the time-saving may be worthwhile for you. This would also allow you to have less expensive CAD operators input the model and deliver the CAESAR input file to the stress analyst. Of course there are also the automatic stress isometric features among others that make this well worth considering.