There are tools for appending RealMedia files, but no easy choices.
Real does have a program for simple editing and appending like this, called RealMedia Editor. But it has not been updated in several years; the last Mac version was for Mac OS 8/9, and it was part of the paid RealProducer Plus download, not the free RealProducer Basic program.
The underlying software for creating and editing RealMedia files, the Producer SDK, is available for Mac OS X from the
HelixCommunity site, but it is not an end-user application; it requires installing the SDK software and using the SDK commands from a terminal window. The SDK is primarily intended for use by commercial applications like Avid Xpress.
Real does provide a free QuickTime export component for converting files in QuickTime-compatible formats to RealMedia. That does not allow for editing or appending of existing RealMedia files, however. The export component is available by choosing Create RealMedia from
RealPlayer 10 for Mac OS X's Help menu.