RRD4J: Change rrd setup for existing items

Hi,

since openHAB 1.7 the setup of the rrd4j data files (e.g. granularity) can be changed in openhab.cfg.

I assume, that changing the configuration does have no effect for existing rrd data files? Is there a way to change the granularity of these files without loosing the historic data?

Thanks for your help!

Juelicher