I don't know if this is really what happened with my chapter. Basically, our situation was that a local group of women wanted to start their own chapter of a sorority, but campus denied them status b/c there were already enough sororities. My chapter decided to see what they had to offer, so we extended an invitation to their leadership to meet with our chapter's leadership and discuss options. Both groups really hit it off, and both wanted to see how to facilitate this. SO, the chapter called me (as an advisor) and I spoke with HQs, and they were fine with us taking on this large group of women and merging our groups, but obviously, we remain D Phi E, and the new women would become D Phi E. After a presentation by myself and other representatives from HQs, we held a sort of pref party for the group to show them how much it meant for us to have them join our group. All 25 of them joined lock, stock and barrel.
Once the bids were signed, major changes took place. The 25 new women did not go through a traditional new member program. The current leadership of both groups were dissolved, and a new leadership was elected for D Phi E from both groups. Sisters who were initiated D Phi Es already were offered the option of early alumnae status if they did not want to participate in this merging situation, and 2 of 15 accepted. The chapter then went through a period called reorganization where everyone went "back to basics" on what D Phi E is, what it means to be a sister, how a chapter operates effectively and efficiently, etc., and this period lasted about a semester and a half. After that semester and a half, the "new" chapter of D Phi E, made up of both groups, went back to regular chapter status. All of the new women were initiated, including not only the 25 women from the original merger, but three new member classes as well, for a total of about 45 women. It was VERY exciting

And now, they function as any regular chapter of D Phi E would normally do.
This was an ideal situation for both groups involved, and one main reason was because the group of 25 girls that joined us did not have a local or national sorority to identify with, and thus, no integration of sorority values, traditions, principles, etc. had to take place. If this opportunity presented itself again, we would definitely look into it. It was a fabulous way for a struggling chapter to get back on solid footing, and all of the women today will tell you that they are so glad they went through the process.
If you have any specific questions, feel free to PM me. But this is my experience