Obviously since all stars by definition changes its chemical composition by the process of fusion the chemical composition is expected to change over time. Elements heavier than iron are produced in a somewhat different manner.
Regarding your second question there is a FAQ from NASA regarding James Webb. Here is one citation of what Webb is capable of in the near-infrared:
"Webb will conduct deep-wide surveys of galaxies in the rest-frame optical and near infrared over the redshift range 1 < z < 6 with both imaging and spectroscopy. The microshutter array, which provides multi-object near-infrared spectroscopy of ~100 targets simultaneously, will allow large samples of galaxies to be divided into bins of redshift, metallicity and morphological structure. "
The instrument for detecting radiation with a wavelength of between 5 and 28 micrometers has another spectrometer that can only focus on four regions simultaneously:
"MIRI uses an image slicer and dichroics to provide imaging spectroscopy over four simultaneous concentric fields of view ranging from 3 to 7 arcsec on a side."
All data collected from James Webb is released to the public one year after it is collected.
Answer: The instrument for collecting radiation in the near infrared region on James Webb up to a wavelength of about 5 micrometers will be used to do more or less automatized categorisation of up to 100 galaxies at the time based on spectrographic redshift, (which is a measure of time) and metallicity (which is basically the chemical composition) and this data is released to the public after at most one year.