Would it be possible to add some kind of slider or other form of option to change the rotation based on health% to focus on death strike instead of frost strike?

You can edit your own priority as you see fit -- it's just not necessarily optimal.

The closest thing I have in terms of instructions is here: https://github.com/Hekili/hekili/wiki/Frequently-Asked-Questions#how-do-i-make-the-addon-recommend-________