Pressure loads are usually not considered to be self-limiting, with good reason. Thought problem - if a pipe is adversely affected by pressure, what mechanism is going to provide the self-relief? I bet you can't answer that.

Pressure elongation is normally not considered in the B31 Code family, so I doubt that you will find any guidance in any of them. Pressure elongation for large bore pipelines is a real effect, but since the B31 Codes do not consider it, I don't believe it is implemented in CAESAR II. You may want to consider doing the calculations by hand.

I am not sure why the Bourdon effect has anything to do with pressure elongation of the pipe. It has to do with the tendency of elbows to straighten under internal pressure (and to curl further under external pressure, a less-common issue). See B31.3 Appendix C Note 7. This note applies only to elbows and miter bends, not to tees.

The only relief you are going to find for your pressure elongation is from axial line stops, and lateral restraints on perpendicular legs. For a line this large, these loads are going to be astronomical. You may want to consider putting pressure-balanced expansion joints in your system to absorb the movement instead. This may well be a less expensive way to control the position of your branch outlets than what you are doing.