I have two FGDB's, both with the same feature classes. I have a hydrants feature class in FGDB 1 that has attachments (pictures) related and want to merge/copy those features to FGDB 2 in its hydrant feature class. Is this possible? I have tried copying the features first, but the global id's change and then the relationship with the attachments do not function properly. I have tried to export the feature class from FGDB 1 to an .xml and then load it into FGDB 2, it says it will overwrite the entire FGDB.
You will need to play with unique/global IDs as an addition to that and establish join first to make it work properly. (Otherwise it won't do it in the right order.) It's not the easiest workaround, but works.