I'd use whatever the dictionary has now, and imagine soon that there will be an added
2. Someone born male who has transitioned to being a woman.
And what does "transitioned to being a woman" mean? They haven't become female, so definition 1 doesn't apply. So it's something else. But you haven't defined it.
And even if we do ever pin down what definition 2 means...
There's no overlap. What do those 2 groups have in common?
This is not like "mother" where 99% of those who fall under meaning 1 (biological mother) also have meaning 2 (primary female carer) apply to them. The dual meaning of the word is productive because 99% of the time both meanings apply.
What's the reason for trying 2 squeeze these two totally disjoint groups under 1 word?
It's like redefining "table" as
1. An item of furniture with a flat top surface raised above the ground, usually on one or more legs
2. headphones with 'table' written on them.
You could certainly do that, but why? You can no longer make any useful statements about tables. You'd have to start saying stupid things like "remember not all tables have legs!". And "but some tables are good for listening to music!".
This would benefit no-one. Apart from headphone manufacturers wanting to get into Which Table magazine. But just because they want it isn't a good idea for everyone else to go along with it.
(And then you'd have the debates about whether What Hi-Fi did table reviews, and whether they were table-inclusive. It would be insane. Yet strangely familiar...
)