Answer: This instruction applies only for paid hosting accounts and requires to EDIT the php.ini file. Inside your web hosting account, PHP Settings menu add the following line at the end of the file:

# For Ioncube and php4:
zend_extension = /usr/local/ioncube/ioncube_loader_lin_4.4.so

# For Ioncube and php5:
zend_extension = /usr/local/ioncube/ioncube_loader_lin_5.2.so

# For Zend Optimizer and php4:
[Zend]
zend_extension_manager.optimizer=/usr/local/Zend_php4/lib/Optimizer-3.3.3
zend_optimizer.version=3.3.3
zend_extension=/usr/local/Zend_php4/lib/ZendExtensionManager.so

# For Zend Optimizer and php5
[Zend]
zend_extension_manager.optimizer=/usr/local/Zend_php5/lib/Optimizer-3.3.3
zend_optimizer.version=3.3.3
zend_extension=/usr/local/Zend_php5/lib/ZendExtensionManager.so
zend_optimizer.optimization_level=15

Answer: Yes however only clients on paid accounts can change certain php.ini settings from their web hosting control panel as well as switch from php 4.x.x.x to 5.x.x.x using PHP Settings menu.