I know in the case of M8, the ROM-included dtb may be device(variant)-specific, but the custom dtb may be universal, so the dtb has to be replaced. The dtb stores some important changes like the overclock values. Is it possible to have an easier way to replace dtb, much like with zImage? I just found this thread and would like to try and use it, but the dtb replacement is essential for these newer HTC devices, for all of the custom kernel to work as intended.
EDIT: Is there a way to check the package for a custom dtb, and if present, use it when repacking, but if not, use the original dtb?
zImages are universal but dtb isn't; luckily copying the file like I explain in the post you quoted is extremely straightforward.
I guess you could check to see if it matches known stock dtb sha1sums, but if it contains the overclock frequencies like you say then it sounds like it'd be necessary to force your custom one regardless.