Confluence 2.5 changed the existing Remote API methods for getting Content Permissions on a Page, and provides a method for setting the Content Permissions on a Page.
This should be documented in http://confluence.atlassian.com/display/DOC/Remote+API+Specification

The relevant methods are

Vector getContentPermissionSets(String token, String contentId) throws RemoteException;
Hashtable getContentPermissionSet(String token, String contentId, String permissionType) throws RemoteException;
Vector getContentPermissions(String token, String contentId) throws RemoteException;
Boolean setContentPermissions(String token, String contentId, String permissionType, Vector permissions) throws RemoteException;