All changes performed on datacollection-config.xml will be reloaded automatically by OpenNMS. So, if we add new metric definitions (manually or using the new MIB Compiler UI), Collectd is going to start gathering data from them without issues.
But, when we try to see the graphs for the new metrics on the WebUI, it is not possible if the metrics in question are related with a new Resource Type (Generic Index Resources).
The reason for this is because the ResourceDao maintains a cache of the internal objects associated with Resource Types which is not updated after modifying the datacollection-config.xml file.
The idea is to add some intelligence to the ResourceDao implementation (i.e. DefaultResourceDao) to check if datacollection-config.xml has been changed and re-create the internal cache with the new resource types.