Using later libs and drivers with earlier WB releases

[paul1981]

I think the ability to load reset-proof resident modules came with Kickstart 1.2 (1987?)

Great for updating OS components, but you'll run into trouble if trying to bolt on later OS release parts as they will likely need higher versions of other libraries / devices themselves (or at least they will version check for it) - either way, a likely failure unless you're happy with loading a long long list of newer modules or the module in question is designed to work with both old and newer releases.

I load a module or two on my 3.0/3.1 Amigas and just the updated scsi.device from the 90's on my 2.0 Amigas (A600's).

[paul1981]

And you are both correct, the limit on using the technique is which exec and intuition library is present at system boot. Those are the 2 you can't mess with by straight replacement, so I've been told.

You've been told wrong unfortunately. Do a search for Piru's exec and Cosmos's exec. OS3.9 has an updated official exec. I do have Piru's 44 beta exec on my hard drive though which I sometimes load. Some people burn custom ROM's too along with many other updated components (exec does need to be first though). Mfilos wrote a nice tutorial here on using Remus to do just that:

http://www.mfilos.com/2010/12/guide-create-and-burn-custom-kickstart.html?m=1