you have to Load all Modules from the Romupdate manually and set the path to your older lib by hand.....
Loadmodules libs:olderlib/myoldlib.library should do the trick...
Setpatch NOROMUPDATES
What I mean is I burned a custom Kickstart ROM with scsi.device 44.2, if I want to try scsi.device 43.43 loadmodule will fail saying scsi device version 44 present. Same issue if you have v43.43 of a library and the library you want to load is 43.45, it will fail saying you have the the same major version.
Loadresident has a FORCE option, but it isn't always reliable-as in the older library sometimes doesn't actually take effect. I'm just thinking it would be better in some cases for Loadmodule to not be "smart" and allow you to force whatever version you want to load.