It was weird for me at first, but I think only from a community sense. I identified as a lesbian to the world from age 12 to 25, though I knew I was trans and wanted to transition at 17. I helped start a GSA in high school. I was a member of Pride Alliance in college and grad school. The majority of my friends are either in the LGBTQ community or are allies. I had been out and gay for more than half of my life by the time I transitioned.
Now. My experience may be different, but at least here the lesbian community was very insular. Everybody knows everybody or at least has the ability to play lesbian phone tree and introduce you to whoever you want to know. It was also very inclusive - no matter how you presented or what you looked like, you were welcome and had a good chance of finding a partner. So the most difficult part was giving this up, knowing that on the flip side the community is smaller, it may be more difficult to get a date, etc.
But it was honest. I think one of the biggest motivators in my transition was the need for honesty. At the time I transitioned, I had known I was trans and that I wanted to transition for about 8 years. That was 8 years worth of not being 100% honest with my friends, family, and the revolving door of significant others that I had during that time. I was not a lesbian. I was a straight, transgender man.
So it was weird to come out and sort of immediately feel like I am not a part of that smaller segment of the LGBTQ community, especially given that there's no real community based around being straight. But I also found that I had less of a need to be a part of a community. I didn't run from the lesbian community to the trans community. I may hang out online in my free time, chat with folks, and offer transition advice but I don't do that out of a need to feel connected to the community, I do it because folks were willing to do that for me when I first started out.
I guess it helped for me to think about what value I was getting from identifying as a lesbian and what I got out of being a member of that community. If you can identify what it is that you're sad about losing/potentially losing, it is easier to figure out what to replace it with.