Say for example you're running php 5.2.11, but wish to roll back to 5.2.2. To do that, you'd edit the versions.txt to specify that version. eg:
cd /usr/local/directadmin/custombuild vi versions.txt
in that file, find these 2 lines
php5:5.2.11:0223d71f0d6987c06c54b7557ff47f1d php5-mail:5.2.11:85a62ef3d069403c29604730e02da9c8
then replace them with the following:
php5:5.2.2: php5-mail:5.2.2:
save and exit the versions.txt.
Next to get the binaries and compile it, type:
./build update_data ./build php n
which will then give you the older version of php5. Restart apache after the compile completes.