Much of it would've been the same as they would've simply tweaked the Ro backstory. Ro would've been a long time resistance member who finally ran away to Starfleet.
They tweaked much of the Trill backstory from TNG to make the Curzon/Jadzia Dax story possible.
That's not comparable at all, as Jadzia was not a crossover character. Miles is a closer comparison (providing familiarity/established affection in the new setting).
I have never heard anything about tweaking Ro's backstory, but rather: Ro was going to be the first officer, when Forbes turned it down, they created Kira to replace Ro, then cast Visitor as Kira.
DS9's overall story was not planned out in advance past the pilot, but was something the writers pulled together and developed over time. Since Kira inspired a large chunk of what they did, it is logical to assume that it would have been very different.