A supernova takes place after several stages occur.
Helium fusion into carbon [ 3He4 > C12] takes the place of hydrogen fusion into helium.
THEN...LATER...carbon nuclei fuse to form magnesium.
And a few more stages occur until iron is formed at the star's core.
Stellar collapse ensues, because iron nuclei resist fusion.

All these stages involve changes in temperature output in the star.
Neutrino activity is also effected.
And there may be changes in the star's spectra with each stage [but it takes thousands of years to convect
those newly created elements into the photosphere, so I'm not confident that changes in a star's spectra offer sufficient
warning of an impending supernova blast.]