I can't see that it is. You always seem to assume that just because a later variant is prototyped in Sinaiticus, it proves something, but here it proves nothing because the early form Βοσόρ is retained:2 Peter 2:15 (AV)
Which have forsaken the right way, and are gone astray,
following the way of Balaam the son of Bosor,
who loved the wages of unrighteousness;
Numbers 22:5 (AV)
He sent messengers therefore unto Balaam the son of Beor to Pethor,
which is by the river of the land of the children of his people,
to call him, saying,
Behold, there is a people come out from Egypt:
behold, they cover the face of the earth,
and they abide over against me:
The true NT Bible word is Bosor, Βοσόρ.
The false NT word is Beor, Βεώρ, a late variant.
Sinaiticus has by the original hand - Beoorsor, Βεωορσορ
A conflation of the two readings.
The evidence here is, once again, Sinaiticus is a late manuscript.
Metzger (2005) Textual Commentary on NT (2 Pet 2:15):
"The reading Βοσόρ, a name not found elsewhere (in fact the Chaldee/Aramaic form of Βεώρ), is strongly
supported by almost all Greek manuscripts, and by most early
versions. The reading Βεώρ, found in B 453 VG(mss), SYR (ph) COP(sa),
is the prevailing spelling of the Septuagint. The singular
reading of Βεωορσορ in Sinaiticus is no doubt due to the conflation
of Βοσόρ with a marginal correction -ewp."