On S4E1&2, Zecora asked Twilight to specifically use alicorn magic to activate a divination potion. Twilight proceeds to use black-purple lightning, like Sombra's.
Can we speculate that Sombra now counts as an alicorn?

Twilight cast black and purple magic in S3 episode 1/2. She was not an alicorn then.
Bam! Done! That'll be 50$

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A relevant discussion from a Skype chat I'm in:

[1:12:34 PM] ocalhoun calhoun: Why did she have to use /that/ magic?
[2:11:00 PM] Csquerade: Did you not pay attention? Use alicorn magic, she said. So she used /that/ magic. 2+2=4, no?
[2:21:41 PM] ocalhoun calhoun: She used that magic before becoming an alicorn. Your argument is invalid.
[2:42:46 PM] Csquerade: Um, no, not at all. A) That can easily be foreshadowing. B) It was also once called dark magic. By also calling it alicorn magic, it can easily imply that the magic is incredibly risky, powerful,
and dangerous to use. C) Do keep in mind that the Alicorn Amulet wasn't used by an alicorn.

In regards to this thread, I think C is the most relevant here.

Since Twilight wielded the same magic back when she was a unicorn, I have to say with no.