So would my origional solution (recompiling every piece of software that needs libcom_err.so.3) be the only "stable" solution?
Yes, that's correct. You either must recompile each application so that it no longer requires the missing library. You actually have the option of installing the old kerberos libraries in an application specific location (perhaps /opt/kerberos-rhl9/) and use LD_LIBRARY_PATH to make sure that they're used:
env LD_LIBRARY_PATH=/opt/kerberos-rhl9/lib ./pine
However, this solution can be much more complicated to get right. In this instance, if I have this right (and I may not, I'm only discussing this for completeness, and not to encourage you to actually do this), you'd need all of the old krb5 libs in that directory, not just libcom_err.so.3.
While pine would load fine with just libcom_err.so.3 in the special library path, kbr5's libs (from Fedora, this time) would also load in libcom_err.so.2. Symbol resolution would be unreliable; sometimes pine would work fine because the symbols in Fedora's krb5 libs would be resolved correctly to those from libcom_err.so.2, and sometimes pine would crash when using Kerberos because the symbols would be resolved to those from libcom_err.so.3.
