Ruthenian or Russian influenced
KRASIŃSKI: root-word krasa (Old Polish for beauty, loveliness); probably toponym form Krasin, Krasna, Krasne or similar.
The inserted-vowel hypothesis cannot be ruled out only insofar as with surnames most everything is possible. Illiterate peasnats often had their names misspelt, mispronoucned and miscopied over the genrations by semi-literate parish priests and village scribes and the Russian partition ordeal certainly left its imprint.
However since Russian also uses the kras- root to mean beauty (eg krasiviy - beautiful, krasavitsa - lovely woman), there seems to be no justification for an inserted -a- except slovenly copying.