Most (all?) scientific ideas are simplifications. e.g. that species are separate. That the relationships between species can be represented by a tree.

Yes, it used to be taught that genes don't change. But there's methylation and telomeres and "gene therapy" is a thing. I agree that changing gene expression sounds like sophistry, since the point of genes is their effect. Sounds like Lamarckism to me.

Everything you've been taught is wrong - in that however thoroughly something is known, there's always more to it.

If you experience stress, your body will upregulate expression of cortisol and other hormones. If you remove the stressor, it will downregulate. Chronic stress can break these processes and require medical intervention. This is all (in theory) detectable with methylation analysis of the genome, but it will take a decade to fully flesh the technology out.

Gene expression is talking about the myriad number of things that causes the DNA strands to relax and unwound from the histone. By exposing that piece of DNA strand the gene can be expressed and the resulting protein is formed. I don’t believe we have a complete understanding yet of what causes genes to be expressed or not expressed. There seem to be multiple factors at play.

My understanding of telomeres is that is primarily a mechanism to prevent cancer. After a cell replicates itself a number of times the telomeres grow shorter and shorter and at a certain point it stops replicating because the assumption is the DNA has now been damaged by environmental factors. Some cells don’t have this mechanism and can replicate infinitely eg skin cells.