The backstory itself isn't very muteable. But, the psychology of the Rowan and Alexia are variable based on choices, and this does extend backwards. In practice, this would produce some small variances in their past relationship. For example, a more MxM inclined Rowan may have had a slightly rockier relationship with Alexia in the past. But, for the most part the past in the same.
I will note that while a Rowan who is 100% homosexual and has no attraction whatsoever to women doesn't really work. But, a Rowan who is much more attracted to men but is repressed is possible. He can be a 5 on the Kinsey Scale, but he can't be a six.