Highly variable elements? Which type of genomic elements in the UCSC browser can be used as an example of the highly labile = highly variable = low conservation regions?
Transposable elements (TEs) are the classic example of rapidly evolving regions in eukaryotic genomes. These are often used as a proxy for neutrally evolving sequences, which are by definition not conserved/constrained. The UCSC genome browser includes various repeat tracks (e.g. RepeatMasker) that includes TEs.

Within protein coding regions, 4-fold degenerate sites are often used as a proxy for neutrally evolving sequences. These sites are where any nucleotide at this position leads to the same amino acid and therefore protein (synonymous mutations).

Potentially even more variable sequences would be those under positive selection, but there is not a single class of element that falls into this category i think.