Forcing yum to reinstall a package.md

When things are OK

# Simply remove and install the package  
yum -y remove PACKAGE  
yum -y install PACKAGE

When things get bad

# Use rpm to force removal and reinstall with yum  
rpm -e --nodeps PACKAGE  
yum -y install PACKAGE

When things go very South

# Trick yum into thinking that the package  
# doesn't exist in the RPM database  
rpm -e --nodeps --justdb PACKAGE  
yum install PACKAGE

N.B. The last method doesn't actually remove any files.

Other notes

Files staged for install when performing a yum update are kept in /var/cache/yum/. This is useful in certain situations.