Icaros allows icon swapping because the "Workbench" is managed by Dopus5 Magellan
I don't think that the Icon.library can solve, i think Workbench.library does it, on AROS 68k I have the same problem despite I use the Icon.Library by PeterK (best ever, supports any icon, OS4, AROS, MOS).
With my AROS One 68k I solved with some old OS3 applications like "IconCopy" and "IconCopier" (see attached video), CopyIcon44 is not supported because it requires OS3.9 libraries, AROS One only supports well old OS3.0/3.1 applications.
OS3.9 does not need any external software for icon swapping, although with the
RAWBInfo improves some features.
OS 3.0/3.1 does not support icon swapping but can do so thanks to the application
SwazInfoAROS One 68k:
Icon Exchange Tutorial Video