I specialize in Twin Flames and soulmates and have been in union with my own Twin for a long time so I'll try to help.
The short answer is sometimes and kind of. I'll explain…
Twin Flames are two halves of the same soul incarnate in two separate human bodies. One half male energy and the other female energy. Twin Flames are Yin and Yang. Twins share certain likenesses but are actually complimentary versus being alike. At least at first. One typically possesses all of the ABC traits and aspects while their partner will possess all of the XYZ traits and aspects. Perfect Yin and Yang meaning that the twins are complimentary.
Upon the time that the Soul Merge takes place; when the two halves of the same soul merge back into one, these complimentary style opposite aspects also begin to simultaneously merge and birth new likenesses. I'll give an example. If both twins happen to like salad (likeness) but one enjoys olives while their partner hates them (opposite) then during dinner, one will eat all the olives so that way no food is ever wasted (complimentaty) so you see, this opposite created a complimentary likeness and a negative dislike of olives becomes a positive compliment and likeness of sharing.
There are physical shifts that occur after Soul Merge as well. While Ideal Romantic Soulmates are typically often mistaken for being so “similar” or even looking related somehow, on the other hand, some Twin Flames experience odd physical shifts. For example, I always had hazel eyes (greenish-blue-brown.) My twin who is the leading twin happens to have been born with pale blue eyes. Upon our Soul Merge, my eye color shifted oddly to his pale blue. It was such an odd synchronicity that people began to notice and inquire if I had begun wearing contact lenses (I had not, of course.)
The Soul Merge occurs when the two halves of the same soul being reunite and merge back into the one, single soul. And yes, it certainly can bring some interesting changes!
I hope this helps! Blessings xo