to somehow corrupt or debase something, to reduce its value, quality, or condition by changing it, especially by adding something new, or broadly, to change something for the worse by adding elements that clash or disagree;
e.g. The chef refused to bastardize a classic dish in such a way.
(verb)
(old) to declare someone to be an illegitimate child (a bastard), or to prove them to be so;
e.g. He threatened to bastardize her child if she revealed the truth.