Is the strain the only value that leads to the word changes? I want to make certain creatures have a steel like skin, but still use the "tearing" and such. I assume that means I can copy all of the steel values except for the strain values, and then just keep the skin strain values?
Just a note here. Urist answered already with his suggestion, but your question totally turned a light on in my own head about a personal mod I've been working on recently. While my thread about upgrading dragon scales will give the whole story, in a nutshell one thing I did is exactly what you asked about, and I wanted to tell you my results.
Thanks to input and advice from others in that thread, I had defined tooth, claw, scale, and bone on my new dragons, with material values that were that of metals; I eventually settled on steel statistics. But of course, dragon against dragon, resulted in a ton of denting and fracturing of scale, but no penetration beyond that whatsoever.
So, first, after reading your question, I removed all the strain values. That resulted in the same issue still, dents and fractures all day long, with one notable difference. The scale strain numbers were such that now, while still never penetrating each other's scale layer's completely, those attacks were now accompanied by a ton of bruising to the fat and muscle layers beneath the outer scale layer. My ultimate solution, if anyone reading is interested, was to just define their claws and teeth as just a tiny bit better than their bone and scale properties, so that they could actually inflict real woulds again.
That's probably no surprise to you, or others, in this thread but I thought I would confirm the strain thing with my own observations of some testing there. I've since decided NOT to define strain values on any creature tissue materials that I define with other properties because, until Urist gave the numbers, there was no way of knowing what those strain values would be. And I'm lazy.
But also, to me it seems a more realistic way to have a tissue, like say scale, mimic a metal, but still have the sort of give that tissues in dwarf fortress have (thus keeping realistic things like bruises happening to lower layers below the scales). Just a way to maintain a little bit of consistency in my own mind at least.
My two cents, for what it's worth